OK, I'm once again stumped. My car just won't idle smoothly. It sounds like it's going to die, but then revs itself up a bit, then almost stalls again, then revs again... So, I thought it might be a vac leak. I had already replaced all of the hoses, but found that I had leaks on the air intake runner things, where they connect to the plennum. So, I disassembled everything, replaced those hose-type things, and voila! No more vac leak there. Problem is, still not idling right. It's just as bad now as before. One more thing, I slowly brought up the rpms from the throttle body, to listen, and I think I heard a couple of really quiet backfires. Maybe an exhaust leak? Could this cause a bad idle? Thanks.

Brian

Mines doin' the exact same thang dammit! and sometimes it won't run unless I pump the gas... sometimes.

Changed the fuel filter hoping that would fix it BUT NO.......

Good weather is on its way & I wanna drive it

........b

vacuum leak ...

did you check the throttle-body itself?
do you have the right (thick) gaskets between the intakes and the heads? did you mount them with sealant?

while the motor is idling, spray some brake cleaner around the suspected areas and see if your idle will change.
but careful, brake cleaner IS flammeable ...

Andy

the intake plenum has been known to fail as well, which will cause vac. leaks

I checked with brake cleaner initially. Thats how I realized I had to take the intakes off and put new hose things on(I have no Idea what their called). After install, I checked again with the cleaner, and no more leak. I did use the proper gaskets, but did not use sealent, but I checked with the cleaner and there seems to be no leak there either. What's the best way to check the throttle body itself? My guess would be to take off the air cleaner, and spray aroung where it meets the plenum. Any other suggestions?

my '73 has allways "hunted" for idle to a very small degree. The guy I trust that works on these things (and owns a pristine '74 2.0) told me thats normal as long as its within 100 or so rpm.

The only things I can think of that you havent tried, is check the vacume lines to the distributor, check the distributor itself.

Not too familer with older FI. On modern FI hunting like you describe is generally a TPS.

Your idle should not "hunt". not even 100rpm. The throttle body must be properly set, then the idle adjustment knob (on the ecu) can be set to the proper CO.

Visit Brad Anders site and read, read, read!

opps, forgot the link

http://members.rennlist.com/pbanders/

I've read, read, read, I just don't always comprehend I've spent alot of time on the FI system, this is the one bug I haven't figured out yet. I set the TPS some time ago, do I need to reset it after fixing vac leaks? BTW, whats the best way to determine if you have an exhaust leak? What are some of the symptoms? Corrections? Thanks.

How did you set the tps?

I used the tech article fm PP with an ohmmeter.

BTW, I still don't understand about the co adjust, but it sounds like something that you have to go to the shop for. I just want to make sure I have everything else that I can do done before doing that. Most of the problems I've had have been relatively simple repairs.

Very good. It should be adjusted right. Be sure to leave some slack in the accelerator cable. You really need a CO meter to adjust it correctly, but you can get it close by ear. Turn the knob on the ecu ccw till it hunts, then back clockwise one click at a time till it evens out. If it doesn;t even out, then something is still not set right. Valves, dwell, timing, and tps must all be in sinc before the ecu knob will work as designed.

The TPS is a varible resistor. What can happen is at the low end the windings will wear out. This can not be fixed by adjustments.

In addition to VSQ's last very good basic tuning advice, check fuel pressure in spec. Often overlooked and assumed correct, if it is off this can make tuning/idle adjust an exasperating experience. If still having problems and can't find a vac leak, how about injector seals?
John

I set the fuel pressure to 29psi. I took the TPS apart before I set it to check the tracks, and it looked good. The car only has 62xxxmiles on it. Where on the ecu is the adjustment knob? Also, all new injector seals, fuel lines, cap, rotor, wires, plugs, fuel filter, valves recently adjusted (they were right on). Just to give a little background, the car sat in a garage from 1987 until this summer when I bought it in an auction.

Not on a FI system in a 914. The d-jet "tps" is actually a bunch of wiper contacts points that the arm slides across, kinda like a rotary switch.



The L-Jet system just has two contacts, one closed at idle and one closed at wide open throttle.


Remember, the D-Jet system was the first practical electronic fuel injection system ever put on a mass produced car.


Bendix developed an Electronic Fuel injection in the late 50s. It actually used Vacuum tubes, and had to be warmed up before the car could be started.

The adjustment knob is on the top left of the ecu. It may have a small rubber cover on it

First set the timing to spec. 27 degrees BTDC at 3500rpms
Secondly, since yours is a 73 2.0l do you have the ballast resistor for the CHT and the right I think its the 017 CHT? You will never get it right if you don't have the right parts.
Then adjust the idle setting when the engine is hot.
There must be no vacuum leaks so all vacuum hoses should be fairly new soft and have a tight fit when they plug in. Like Andy said use a brake cleaner to test for leaks.
Test the AAR valve to make sure its closed after 5 minutes of running. These things tend to rust inside and not close or open.
Now adjust the idle rpm with the air bypass screw and the idle mix adjustment on the ECU as VSG914 said. You should have one or its been swapped out.

Geoff

with what Geoff just said. A hunting idle is often caused by a lean mixture. Once you're sure everything else is good, adjust the ECU. Sounds like you're getting very close.

An exhaust leak will usually backfire. I had a bunch of leaks where the heat exchanger bolts up to the head. If you stick your head down there with the car running, you can hear it backfiring, and can see or feel exhaust blowing out as well. When I had exhaust leaks, it caused a pretty eratic idle. It probably wouldn't hurt to crawl under and make sure everything is sealed up. I can't remember the correct torque for the nuts, off hand.

I do need a new AAR. Mine does not open all the way when cold. It does close when hot however. I think I will double check the TPS, and climb under and try to figure out whether or not I have exhaust leaks. If I do, is it normally just a matter of tightening bolts? Time to go get a little dirty.

Brian

The AAR shouldn't cause a problem with the idle when warm. The cat might idle a little low when cold, if the AAR isn't opening all the way, but it should have no effect when warm.

Crawl under and check to see if you can feel or see any exhaust leaking out around the head. If so, try torquing the nuts. I can't remember what they should be torqued to, but it's not very high. Be careful when tightening, as the studs have a tendancy to break. When I do it, I start at a lower torque setting, and slowly work my way up to the max torque.

Hopefully somebody will post the correct torque. If not, I know I've asked before.

Check out this thread on exhaust leaks.

exhaust leak thread

Mike,

Thanks for the link. I do feel some hot air coming down from somewhere in the vicinity of the heads, but not sure if it's pulsing or steady. I have very little experience (OK, none at all) with exhaust systems. I'm a little lost on some of the terminology. It appears that there are 2 round tubes on either side that bolt up. I imagine these are the most likely locations of exhaust leaks. The ones more to the front of the car are pretty well shielded. Is it just a matter of removing engine tin up there to get at it? Am I missing something? Thanks.

To get to the exhaust stud nuts remove the tin surrounding the exchangers. Those flat headed screwdriver slotted screws hold them on. sometimes they need a little persuading. A BIG screwdriver really helps. If I remember right there are just 2 per side. Once removed its pretty much open to get a socket on the nuts. The torque on them is 14 lbs. Good luck.

.....b

I don't use a torque wrench on exhaust studs unless it's a new head and studs, and then work your way slowly up the torque scale. They can and will break off. Just do it by hand . You just have to have the "feel" to know when to stop. If they are loose you will know it. Oh, a wobble type extension is the best tool to use.

Thanks. I got the tin off on one side, but the drivers side piece is on there to stay. I sprayed some liq wrench, hopefully it'll come off easier when I try next. Are there any other locations I could have a leak from?

I got up under there, and made sure everything was tight where it bolts to the head. All seems good. I got back under with the car running, and I can't see, hear, or feel any leaks. My muffler is awfully loud though. I double checked my fuel pressure, and timing (both are fine) double checked for vac leak (nothing). I tried adjusting the ecu, it seems a little better when I went about 4 clicks ccw. Still not a nice steady idle. Any further thoughts???? I'm getting desperate.

Could a bad injector be causing all of these symptoms. I was reading an old thread that suggested similar muffler noise/backfiring, but didn't mention any strange idling. Just a thought.

Dont listen to these guys, they're all wrong. The real reason your car wont idle is because it is a 914 They never idle right

he's right! Had you goin!


M

Yup, we're all doomed to eratic idling.

Hmmm, turning the ECU knob ccw should lean out the mixture. Usually a lean mixture causes hunting. Did you try turning it cw? What happened when you did?

How does the car accelerate? Is it just at idle that it runs poorly? If so, then it's not likely an injector, although it is possible. You could try pulling off spark plug wires one at a time. If you pull on off and there is no change in the idle, then there is something wrong with that cylinder. Either fuel or spark.

Another thing to check is your MPS. Does it hold a vaccuum? Also, how much vaccuum is your engine pulling at idle? I believe it should be around a steady 15in/hg at idle.

I'm kind of starting to guess here, but keep posting and I'm sure we can figure this out. I know how frustrating it can be, I've been there myself.

How do I test to see how much vacuum I'm pulling at idle? Is testing the mps the same? Also, the muffler is really loud at idle. When the car accelerates, it quiets down, and seems to run well. When I turned the ecu cw, it seemed to make the idle worse. ie. the searching more pronounced. I will go try pulling the wires. Thanks for the suggestions Mike.

Brian

To test vaccuum, you need a vaccuum gauge. I bought one, but most local FLAPs will loan them out. First of all, pull a vaccuum on the MPS, around 15in/hg, I think. If the vaccuum drops, it needs to be fixed or replaced. I believe the acceptable levels are listed on Brad Anders page, I can't remember them off the top of my head.

If the MPS checks out good, then just T in the vaccuum gauge in the line that goes to the MPS. The engine should pull a steady 14 - 15in/hg at idle. If the gauge fluctuates too much, that could cause an unsteady idle. At this point I'm pretty much guessing, but these are pretty easy things to check.

Let us know how it goes.

Awesome, thanks again Mike. I'll have to go pick one up when I get a chance. This problem is driving me crazy.

I would check the CHT first!! It is not expensive to just replace it and see!

Jeff

Is it easy to test, or should I just buy a new one. I think they're about $40 at PP. BTW, where exactly is it located?

Just thought of something that may/maynot have anything whatsoever to do with this. My cold start valve when connected floods the engine. Therefore, I do not connect the elect to the injector there. The fuel line is pressurized and does not leak through the injector. I don't know what sends signals to that injector, but it must be messed up. Could this have anything to do with my poor idle? Thanks again.

Brian

The cold start injector shouldn't affect anything. I believe the way it works is this: There is a temp sensor on top of the case, on the passenger side, near the front. That senses the temp of the case. If it's cold, it activates the cold start injector. As far as I know, the cold start injector should only be activated when the engine is cranking, and should shut off when the engine is running. I suppose that if the wire to the temp sensor fell off and is grounded, the cold start might run all the time, and who knows, it could do something funky.

I don't think I have any pics of the cold start sensor off hand. I think there might be one on Brad Ander's page. It wouldn't hurt to try and get it working right.

That would make sense. I will have to try to find that sensor. Thanks.

Sorry, I couldn't find a pic of it, but if remember right, it's almost right behind the dizzy, down low, attached to the top of the case. It's probably easier to get at with the air box removed.

UPDATE-

It turned out to be a leaking injector. Replaced it, and it's now running great. Thanks.

Way to go! I knew you'd figure it out eventually.

Still plenty more to do, but at least it's running. Doesn't start too well, but hey, it's on its way. Thanks again Mike.