Surge / Idle Options

[lsintampa]

75 2.0 FI

I'm in Florida - so the weather outside is somewhat warm (50's maybe right now).

I'll try to be as detailed as I can. I've had this issue since I started driving the car - about 8 months ago. It underwent a motor rebuild - along with some other mechanical repairs.

All hoses are new (air supply, and fuel). ECU and other FI components are original - best I can tell.

When I start the car - it starts right up. At idle RPMs go to about 1500 with a very slight surge (maybe 1450 - 1550).

If I pull the air supply that goes to the AAR from the air filter and plug it, the idle goes down to what I'd expect - about 900 RPM still with a little surge. This is while the motor is "cold" - so to speak. Within like a minute of starting.

As the car warms - just at idle, the RMPs start to come down and the vacuum from the AAR isn't as strong - but still present. However now the surge is crazy - like from almost a stall up to maybe 1200, back down, back up, etc.

Pulling the hose from the AAR - does nothing - I can plug it or leave it and the air filter wide open and there is no change. I put the hose back on - again no change.

I did not let it get to a full warm state - IE the temp gauge just started to move up.

I've heard there are three states (cold, pre-warm, and fully warm) that come into play.

Various tinkering, like turning the air mixture valve to a total closed state, and mucking with the ECU dial has had some success, but at BEST, I get like a 1200 RPM idle still with some surging.

To the best of my knowledge there are no air leaks - at least not from any hoses.

I've some concerns that the air plenum may have some stress cracks around the support studs. But I don't know that would cause the surging? I'd think the idle would just be high - period. YES / NO?

I don't know where to begin to figure out why it behaves this way.

Thanks,

Len

[76-914]

"To the best of my knowledge there are no air leaks - at least not from any hoses."

Well, you need to "know" because your the mechanic. I chased this same scenario for months before I found one of the new injector seals had not sealed because I inserted the injector at an off angle so to speak. Once that was addressed I found that the MPS was also out of tune since the rebuild. Installed an AFR gage, tuned the MPS and all was great.

EDIT-Pull that plenum and inspect it. Pour some liquid into it to see if there are any leaks at suspected areas, check intake runner hoses, oil filler gasket, throttle shaft for excessive wear. Also, disconnect everything from the vacuum source except the MPS. If it runs better re-attach each item, one at a time until you find it.

[JawjaPorsche]

"To the best of my knowledge there are no air leaks - at least not from any hoses."

Well, you need to "know" because your the mechanic. I chased this same scenario for months before I found one of the new injector seals had not sealed because I inserted the injector at an off angle so to speak. Once that was addressed I found that the MPS was also out of tune since the rebuild. Installed an AFR gage, tuned the MPS and all was great.

EDIT-Pull that plenum and inspect it. Pour some liquid into it to see if there are any leaks at suspected areas, check intake runner hoses, oil filler gasket, throttle shaft for excessive wear. Also, disconnect everything from the vacuum source except the MPS. If it runs better re-attach each item, one at a time until you find it.

Oil filter gasket. Does any vendor sell this? I did not see it on 914Rubber website.

Thank you in advance for your response.

Merry Christmas!

[BeatNavy]

Oil filter gasket. Does any vendor sell this? I did not see it on 914Rubber website.

Thank you in advance for your response.

Merry Christmas!

I've had similar symptoms (crazy up and down surge) when the vacuum line to my PCV valve is disconnected or not sealed tightly. 914Rubber does sell that gasket. You're talking THIS ONE, right?

[lsintampa]

"To the best of my knowledge there are no air leaks - at least not from any hoses."

Well, you need to "know" because your the mechanic. I chased this same scenario for months before I found one of the new injector seals had not sealed because I inserted the injector at an off angle so to speak. Once that was addressed I found that the MPS was also out of tune since the rebuild. Installed an AFR gage, tuned the MPS and all was great.

EDIT-Pull that plenum and inspect it. Pour some liquid into it to see if there are any leaks at suspected areas, check intake runner hoses, oil filler gasket, throttle shaft for excessive wear. Also, disconnect everything from the vacuum source except the MPS. If it runs better re-attach each item, one at a time until you find it.

Well, here's an odd one for you all to ponder.

I adjusted the throttle valve switch - per the Pelican instructions - had no effect.

So with the motor warmed up now - AAR is shut down, for kicks I pulled the hose off of the MPS leaving it open to the plenum.

Would you know it, the surging stopped instantly, and plugging the hose only dropped the idle a bit more.

No clue what that means - other than the MPS is not working correctly???

[JawjaPorsche]

Oil filter gasket. Does any vendor sell this? I did not see it on 914Rubber website.

Thank you in advance for your response.

Merry Christmas!

I've had similar symptoms (crazy up and down surge) when the vacuum line to my PCV valve is disconnected or not sealed tightly. 914Rubber does sell that gasket. You're talking THIS ONE, right?

Thanks for responding. I have replaced that one. Is there a gasket for the screw on top?

[BeatNavy]

Thanks for responding. I have replaced that one. Is there a gasket for the screw on top?

Oh, do you mean the sealing ring, number 1 below (Part Number: 021 115 137)?

Yeah, that seems to be NLA all over.

[JawjaPorsche]

Thanks for responding. I have replaced that one. Is there a gasket for the screw on top?

Oh, do you mean the sealing ring, number 1 below (Part Number: 021 115 137)?

Yeah, that seems to be NLA all over.

Might be a gasket 914Rubber will consider making for us. Fingers Crossed!

[DRPHIL914]

"To the best of my knowledge there are no air leaks - at least not from any hoses."

Well, you need to "know" because your the mechanic. I chased this same scenario for months before I found one of the new injector seals had not sealed because I inserted the injector at an off angle so to speak. Once that was addressed I found that the MPS was also out of tune since the rebuild. Installed an AFR gage, tuned the MPS and all was great.

EDIT-Pull that plenum and inspect it. Pour some liquid into it to see if there are any leaks at suspected areas, check intake runner hoses, oil filler gasket, throttle shaft for excessive wear. Also, disconnect everything from the vacuum source except the MPS. If it runs better re-attach each item, one at a time until you find it.

(IMG:style_emoticons/default/agree.gif)
its either a vac leak you have not found OR you are still running lean so ild will be high, and if it goes lower it will start to surge.
lean running, could be CHT issue and/or MPS but probably with MPS - is the MPS a stock original?( they tend to be a bit on the lean side) - oh, then of course re-verify your timing if you have not already.

pw

[lsintampa]

"To the best of my knowledge there are no air leaks - at least not from any hoses."

Well, you need to "know" because your the mechanic. I chased this same scenario for months before I found one of the new injector seals had not sealed because I inserted the injector at an off angle so to speak. Once that was addressed I found that the MPS was also out of tune since the rebuild. Installed an AFR gage, tuned the MPS and all was great.

EDIT-Pull that plenum and inspect it. Pour some liquid into it to see if there are any leaks at suspected areas, check intake runner hoses, oil filler gasket, throttle shaft for excessive wear. Also, disconnect everything from the vacuum source except the MPS. If it runs better re-attach each item, one at a time until you find it.

(IMG:style_emoticons/default/agree.gif)
its either a vac leak you have not found OR you are still running lean so ild will be high, and if it goes lower it will start to surge.
lean running, could be CHT issue and/or MPS but probably with MPS - is the MPS a stock original?( they tend to be a bit on the lean side) - oh, then of course re-verify your timing if you have not already.

pw

Checked timing... maybe you missed my last reply - If I pull the hose off of the MPS - the car seems to idle just as I'd expect. Put the hose back on and the surging kicks right in.

[BeatNavy]

Another case of a car running better without the MPS??

If that's the case, then you probably are running super lean due to some major vacuum leak and removing the MPS is making the mixture "acceptably" richer to compensate.

The only time of had that kind of surging is when I've forgotten to reconnect a hose or make sure it was tight.

[r_towle]

its a vacuum leak

[DRPHIL914]

"To the best of my knowledge there are no air leaks - at least not from any hoses."

Well, you need to "know" because your the mechanic. I chased this same scenario for months before I found one of the new injector seals had not sealed because I inserted the injector at an off angle so to speak. Once that was addressed I found that the MPS was also out of tune since the rebuild. Installed an AFR gage, tuned the MPS and all was great.

EDIT-Pull that plenum and inspect it. Pour some liquid into it to see if there are any leaks at suspected areas, check intake runner hoses, oil filler gasket, throttle shaft for excessive wear. Also, disconnect everything from the vacuum source except the MPS. If it runs better re-attach each item, one at a time until you find it.

(IMG:style_emoticons/default/agree.gif)
its either a vac leak you have not found OR you are still running lean so ild will be high, and if it goes lower it will start to surge.
lean running, could be CHT issue and/or MPS but probably with MPS - is the MPS a stock original?( they tend to be a bit on the lean side) - oh, then of course re-verify your timing if you have not already.

pw

Checked timing... maybe you missed my last reply - If I pull the hose off of the MPS - the car seems to idle just as I'd expect. Put the hose back on and the surging kicks right in.

yes- i admit, jumped to the reply before reading down thru all of the responses-

Another case of a car running better without the MPS??

If that's the case, then you probably are running super lean due to some major vacuum leak and removing the MPS is making the mixture "acceptably" richer to compensate.

The only time of had that kind of surging is when I've forgotten to reconnect a hose or make sure it was tight.

maybe- and a bad vac leak like rich suggested could dot his - in my case recently it's the MPS gone bad electronically, making it SUPER lean, so disconnecting the mPS makes it default rich, but in this case still run

[BeatNavy]

"To the best of my knowledge there are no air leaks - at least not from any hoses."

Well, you need to "know" because your the mechanic. I chased this same scenario for months before I found one of the new injector seals had not sealed because I inserted the injector at an off angle so to speak. Once that was addressed I found that the MPS was also out of tune since the rebuild. Installed an AFR gage, tuned the MPS and all was great.

EDIT-Pull that plenum and inspect it. Pour some liquid into it to see if there are any leaks at suspected areas, check intake runner hoses, oil filler gasket, throttle shaft for excessive wear. Also, disconnect everything from the vacuum source except the MPS. If it runs better re-attach each item, one at a time until you find it.

(IMG:style_emoticons/default/agree.gif)
its either a vac leak you have not found OR you are still running lean so ild will be high, and if it goes lower it will start to surge.
lean running, could be CHT issue and/or MPS but probably with MPS - is the MPS a stock original?( they tend to be a bit on the lean side) - oh, then of course re-verify your timing if you have not already.

pw

Checked timing... maybe you missed my last reply - If I pull the hose off of the MPS - the car seems to idle just as I'd expect. Put the hose back on and the surging kicks right in.

yes- i admit, jumped to the reply before reading down thru all of the responses-

Another case of a car running better without the MPS??

If that's the case, then you probably are running super lean due to some major vacuum leak and removing the MPS is making the mixture "acceptably" richer to compensate.

The only time of had that kind of surging is when I've forgotten to reconnect a hose or make sure it was tight.

maybe- and a bad vac leak like rich suggested could dot his - in my case recently it's the MPS gone bad electronically, making it SUPER lean, so disconnecting the mPS makes it default rich, but in this case still run

Phil, from what I recall on yours you solved it with a spare MPS, right? Did you test the continuity at primary and secondary coils (terminal pairs) and still get acceptable readings (i.e., did you verify the MPS failed by testing it or by discovering that a replacement MPS worked)?

[lsintampa]

Well, it's about as good as I can get it.

Everything hooked up, when warm.. the idle surges between 1100 and 1200. High but if I try to get it any lower it just gets worse.

It will need to do for now until I find someone that knows how to figure it out.

I can do a bit - follow directions, etc., but I'm no expert for sure.

As far as vacuum leaks, about the only thing I can suspect would be the plenum. I checked the FI seals (all new) - reseated them. Just about all the other seals are new - as are the hoses.

Not sure if it matters, but the car WAS from CA - and had other parts that are long gone. Not sure if it had a speed limiter or not - I have the resistor pack that I think went with. The FI harness is from a 2.0 D-Jet - NON-CA car. Maybe something to do with it?

I've had one issue after another - trying to get this car settled down. Little seat time, but what time I've had has been GREAT. The issue only shows up at idle - car runs great - doesn't cut out, no issues with any backfires, misses, etc.

I think I'll enjoy it for a bit and drive it. Maybe when I get up enough energy to take the plenum off (again), I'll check it out.

[DRPHIL914]

"To the best of my knowledge there are no air leaks - at least not from any hoses."

Well, you need to "know" because your the mechanic. I chased this same scenario for months before I found one of the new injector seals had not sealed because I inserted the injector at an off angle so to speak. Once that was addressed I found that the MPS was also out of tune since the rebuild. Installed an AFR gage, tuned the MPS and all was great.

EDIT-Pull that plenum and inspect it. Pour some liquid into it to see if there are any leaks at suspected areas, check intake runner hoses, oil filler gasket, throttle shaft for excessive wear. Also, disconnect everything from the vacuum source except the MPS. If it runs better re-attach each item, one at a time until you find it.

(IMG:style_emoticons/default/agree.gif)
its either a vac leak you have not found OR you are still running lean so ild will be high, and if it goes lower it will start to surge.
lean running, could be CHT issue and/or MPS but probably with MPS - is the MPS a stock original?( they tend to be a bit on the lean side) - oh, then of course re-verify your timing if you have not already.

pw

Checked timing... maybe you missed my last reply - If I pull the hose off of the MPS - the car seems to idle just as I'd expect. Put the hose back on and the surging kicks right in.

yes- i admit, jumped to the reply before reading down thru all of the responses-

Another case of a car running better without the MPS??

If that's the case, then you probably are running super lean due to some major vacuum leak and removing the MPS is making the mixture "acceptably" richer to compensate.

The only time of had that kind of surging is when I've forgotten to reconnect a hose or make sure it was tight.

maybe- and a bad vac leak like rich suggested could dot his - in my case recently it's the MPS gone bad electronically, making it SUPER lean, so disconnecting the mPS makes it default rich, but in this case still run

Phil, from what I recall on yours you solved it with a spare MPS, right? Did you test the continuity at primary and secondary coils (terminal pairs) and still get acceptable readings (i.e., did you verify the MPS failed by testing it or by discovering that a replacement MPS worked)?

kind of , yest - tried the spare and the car started and runs, albiet still on the lean side - and ses tested the termial pairs and they tested o.k.( 92 and 330 ohms on static ). - My mechanic put his hand pump vac withmeter on it( the old one) while running but vac line off of it, so it was running but super rich and began to draw pressure and only got to 5mmhg and it killed it, AF meter wen super lean that fast. - - which appears to indicate that electronics inside were somehow bad, not the diaphragm. btw that unit had nevere been opened but a p.o. had drilled a hole thru the epoxy plug and cap to access the center screw to adjusted it, so i think it may have been going bad for a while and maybe that was able to compensate-for a while at least. and one thing i had not done was to test that resistance under a load . i just assumed that it was o.k. becasuse it was good static and held vac.

[saigon71]

Have you replaced your TPS board with a new one?

My 74 2.0 D-jet had the same issue. After verifying that I had zero vacuum leaks, timing/dwell spot on, good MPS, new CHT with correct part number and adjusting TPS per Pelican article...I still had the same problem.

I bought a new TPS board from Dave Sprinkle, a member on this forum, installed it and calibrated it according to the Pelican instructions. It fixed the idle surge. Car now idles perfectly throughout the entire warm-up cycle.

[r_towle]

Well, it's about as good as I can get it.

Everything hooked up, when warm.. the idle surges between 1100 and 1200. High but if I try to get it any lower it just gets worse.

It will need to do for now until I find someone that knows how to figure it out.

I can do a bit - follow directions, etc., but I'm no expert for sure.

As far as vacuum leaks, about the only thing I can suspect would be the plenum. I checked the FI seals (all new) - reseated them. Just about all the other seals are new - as are the hoses.

Not sure if it matters, but the car WAS from CA - and had other parts that are long gone. Not sure if it had a speed limiter or not - I have the resistor pack that I think went with. The FI harness is from a 2.0 D-Jet - NON-CA car. Maybe something to do with it?

I've had one issue after another - trying to get this car settled down. Little seat time, but what time I've had has been GREAT. The issue only shows up at idle - car runs great - doesn't cut out, no issues with any backfires, misses, etc.

I think I'll enjoy it for a bit and drive it. Maybe when I get up enough energy to take the plenum off (again), I'll check it out.

Best test is to go to the hardware store and buy an assortment of rubber caps.
Remove every line from the plenum (after the car is warm) and cap them with the tight rubber caps.
See if idle stablizes.

I ran into this early on in my car, so over 10 years ago.
I found that the manifold to intake runners develop a slight vacuum leak.
I now put them on with RTV gasket at the head side and at the manifold side and I let it setup overnight before running the motor, leak gone.

I also round leaks at the decel valve (I removed it forever)
I found leaks at the AAR valve, (removed it forever)

From there I found that there is only one way to set the TPS properly, and there is no possible variation. It must sit in a certain position at Idle, or its wrong.

If its wrong at idle, it surges, but it also makes the car run wrong all over the place, but its hard to notice except at idle when it surges.

Oh, one more thing I found was the distributor advance plates need to be cleaned and lubed because they have 40 year old grease that now behaves like glue when hot...and when the advance plates do not snap back to zero advance, the car surges at Idle.


Let me see if I have the pic

rich

[r_towle]

Here

[r_towle]

sorry, had to get it off my phone.

See the middle brass contact finger?
See how it is touching nothing?
That is what it must look like at idle.

The one one the left sits on the first leg.

I found it alot easier to remove the throttle body along with the TPS and set it when its not in the car, so you can see everything clearly.

Rich