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

"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!

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?

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???

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.

Click to view attachment

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

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.

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.

its a vacuum leak

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


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)?

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.

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.

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.

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

Here

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

If you are talking about the one with the blue arrow pointing to it, that seems to be on something? I'll have to pull that puppy off and take a look.

the reason the TPS can be adjusted is it was made for a large number of cars.
At the end of the day, it can only be positioned ONE way to work on a given throttle body.

The idle circuit is a special circuit in the ECU, so it needs to have the TPS in the correct position in order to make that special circuit activate.

Does the idle mixture screw on the ecu make any difference?
Have you verified dwell and timing?

Dwell and timing were checked a while back. No big changes to think they are off, but I can check it again.

ECU adjustments .... I've turned that thing all the way in one direction and the other. Seems to make no difference. I don't know how sensitive that ECU adjustment is, but it seems to me that it really doesn't do much.

I removed the Throttle Body and adjusted the switch using the Pelican method. At full CCW it reads 1 OHM, then I turn clockwise to Zero, then ONE more notch - OHM meter is still at ZERO at that point. Didn't seem to do much.

I opened the air valve on the TB so my idle goes up to like 1500 RPM. At that speed, the surge is minor, but still present. Seems to get really wild (surging) when I try to turn in the air valve on the TB - the lower the RPM the worse the surge.

IDK, It would be nice to figure out. I'm just not in the mood to yank the whole system out to check that plenum. I still think (and I'm most likely wrong) that if there were a air leak, the idle would just go high. Something I don't understand is going on. (as he states the obvious)

The idle mixture knob will work only if the tps is correctly set. Your tps board is crap. Contact Dave sprinkle for a new board. They can ohm correctly but still not work.

I was still having a bucking at 2800-3000 rpm and issue with not having a steady idle. I had replaced the board a few years ago with one of Dave's but it did go bad too. I got a very lightly used original tps from Bruce stone and both of those issues are now gone completely and once the tps was put in right place- I used the picture that rich posted above, the ecu know will increase or decrease your mixture and effect your idle for sure. I think I counted 22 or 23 clicks so put in the middle and start from there.

Before you buy anything, please LOOK at the TPS as mounted, at idle, with the cover removed.

Here is one

http://www.914world.com/bbs2/index.php?sho...lates++cleaning


Someone did a thread with pictures that may help more if you find it.


This
http://www.914world.com/bbs2/index.php?sho...lates++cleaning

I have gotten a few years extra life from a tps by sanding the traces on the board with 2000 grit wet or dry, then cleaning with lacquer thinner

Well, here are two shots of how the throttle switch is set.

I've not tried this setup yet, as I just took the TB off to set it.

I'm thinking it's right on - but I don't know for sure.

In any event, I'm going to give it a shot.

And so it goes.


Click to view attachment


Click to view attachment

If the middle finger is "touching nothing" about the only way I could get it there was to take the TB off the car, then used a OHM meter to insure the finger was not touching the "brass tracers".

The pictures I just posted - the middle finger WAS still touching. So I made just a slight adjustment - used the OHM meter to insure it was not touching and installed that into the car.

To be honest, the surging is now worse than it was.

Question... would the Dizzy vac be suspect? Or the Dizzy advance plates?

The Dizzy is original - just new points / condenser....

The other suspect is still the Plenum.

Onward through the fog....

when i went thru this first time, i did have leak at the plenum and at the throttle body, and put on new hoses for the intake runners-to-plenum, but those still leaked, so i put clamps on those and now no vac leaks at the TB, plenum or intake runners.
test by spraying a bit of water mist or some use carb cleaner- that will richen and change your idle if it is leaking.

YES
YES

clean the distributor advance plates, I believe I posted a few threads above in this thread....go look at that.

IF you are diagnosing, take your time to see if you are doing something worthwhile.
So, when you take apart the advance plates, take your time, do they move and spin freely in your hand before you seperate them, or is there friction and binding???

Try to note the before and after condition so next time it happens, you know.

BTW, if the advance plates have never been cleaned, they will bind and in some cases be very hard to move, even cold.
When you grease them and clean them....you will be amazed how easy they move.


rich

Well carrying on with the experiment....

Since the last setting of the TB switch caused the surge to get worse, I went back to old school and adjusted it using the Pelican method, and now the surge is much improved, but still persists.

That in itself has to be a clue ?? or not, I guess.

I'm gonna try the carb cleaner trick - poke about the fuel runners, plenum, etc. See if there is some suction happening where it shouldn't.

I'm beginning to think that perhaps the dizzy may be the next component to inspect.

But as it pertains to the dizzy, I'd think if the advance / retard were not functioning correctly, I'd have issues while driving up and down the RPM range. Car runs fine at speed, so that's why I've not suspected that the dizzy was suspect. Can't hurt to check it out though.

Maybe I'm onto something here....

I don't have any carb cleaner, but I do have starter fluid and a fire extinguisher

With the idle surge as good as I can get it, I started up at idle and started spraying about areas where no air should enter.

Left side fuel runners - nothing - no change. Right side however did change the idle. At first I thought it might be the fuel runner gaskets, but I don't think so.

The runner gaskets, manifold gaskets, TB gasket, all are new, as are the injector seals. So I don't think that's the issue.

HOWEVER, I do now suspect the plenum itself is an issue. I had asked this once before, but I wasn't really sure if my question was understood.

Simply put, there are two support tubes (columns) that support the plenum. They are on opposing sides, and the tubes are hollow - they go directly through the plenum. I recall that MY tubes are "loose" - by loose, I mean I can turn them, the ends are not connected to body of the plenum. They don't fall out, but they certainly are not "welded" to the plenum body.

I'm thinking the plenum needs to be taken out - OUCH - and repaired. ???? No / Yes?

Is there an easy way to get that puppy out without having to remove the manifolds? I guess I could cut the runner gaskets. Not sure how easy it would be however to put new ones on - once I yank that puppy.

sounds like you probably found your leak, those should not be loose. Get ahold of Bruce Stone, he will have a nice newly powdercoated one most likely or have one done for you - in the mean time can you tape over those to seal them off just to test it?
Phil

put four large screw clamps on the rubber between the intake runners and the plenum, see if those are leaking.

As far as taking it off goes, well without the rubbers its about 1/2 inch or more away from the intake runner tubes, so if you can slide the rubbers back, you can do it...even if its just one side, then pull if off the other side.

Beware, you may need to buy new rubbers which I believe are NLA, so shop around for that first to make sure you get new ones the correct diameter before you shred them.

Rich

I just ordered new rubbers from Pelican - seems they still have some. Not sure what I'm going to do next though. I'll have them if I need them.

I'm gonna try the hose clamp thing - but not until the holidays are over - it's getting nuts around the house - and I'm not about to go shopping - that's a given.

Will revisit this in a few days...

Thanks for all the input.

Happy Holidays - !!!!!

buy a can of carb cleaner....its safer than starting fluid....

rich

2L intake runner sleeves are still available. 1.7 are not.

Len,

Try the new manifold-to-plenum seals like Rich said. If you still have a leak, let me know and I can weld the plenum for you. Or you can buy a purty one from Bruce - he's a great guy and his stuff is always pretty.

Put 8 clamps on the fuel tubes - no difference.

George, I just sent you a PM.

Taking the plenum out isn't really on the top of my list, but I don't really know what else to do.

Tried to tape those support holes - and you really can't reach the bottom ones. So trying that is out.

if you can get your hands on a smoke machine, a halloween fog machine, you can blow smoke into the intake system to see if you can find a leak

If you figure 15 small leaks add up to one large leak, it may help

Yeah, I think I understand what you're saying. The idle circuit is not even working if that middle finger (no pun intended) is making contact. (I think this is what you said). And if it IS touching something, you end up with a high idle - me thinks.

With how my switch is set up it need to go nearly fully CCW to be "set". Seems odd to me as well, but it is at the CCW limits in order to get that middle finger off any tracers.

I dont remember the schematic
Look at Panders site and see exactly what the readings need to be, on what pin at the ECU end of the wiring loom and see if its correct when the TPS is at idle.

Subscribed

One reason for my confusion is that this diagram of the ECU circuit part that shows the TS clearly states that pin 17 should be in the "closed" position during idle. See upper left corner of the diag.

Pin 17 is the Middle finger you're showing as "touching nothing" at idle. (My translation is open).

I'm neither a mechanic or circuit master, but just looking at how the fingers (especially the middle one) travels on moving the throttle, says that at ANY position - other than "at idle" puts that middle finger in contact with the trace. SO, my common sense tells me that pin 17 should be OPEN at idle. Which is in agreement with what you are saying - and in opposition to the drawing.

Am I missing something?


Click to view attachment

Post a pic of your tps, but your logic is correct.
Idle is one position on the switch, open or closed.

It's a conditional switch.
At idle it's condition A
Rest of time it's condition B

You need to make sure condition A works.
That is how the tps needs to be set, so idle works.
The rest follows that baseline position properly.

Easy test, get it warm, get the idle fluxuating, unplug the tps.

I am still leaning toward distributor advance plates are dirty....I believe you mentioned they have never been cleaned, and yet you have not done that yet.
Small vacuum leaks also add to the mix.
Rich

This is the current setting - not tested.

Click to view attachment

Well pulled of the dizzy...

After removing the vacuum - the top plate doesn't bind or get stuck in any position.

I'm going to go over the other threads about the dizzy plates and just make sure that I'm OK on the dizzy side of the ocean.

That said, I could use a new o-ring anyway. So there's that.