Idle Issues
 

After a bunch of WOT runs yesterday, car failed to idle properly and basically dies.

I've addressed all the common stuff so far - changed FPR, TPS, new fuel pump, replaced ISV, DME temp sensor, checked/cleaned cap and rotor and I'm at the point of pulling my hair out!!

All vacuum lines and hoses are new and for the life of me, I can figure out why this car won't idle. Car was running flawlessly prior to WOT runs.

The engine will run absolutely smooth when the throttle plate is just off the TPS "click", but if idle is fully closed the car will die.

Thoughts please.

A hose probably came off when you were doing the wot runs, same thing happened tome on wednesday. Check all the hoses where you can possibly have boost leak.

Do this test loosen up the tps bolts so you can turn it. Now get the car to idle with the throttle of the tps click point. It should idle ok as you have stated. Now rotate the tps to make it click(keeping the throttle constant), does the car die or does it keep idling ?
Sox

Hoses are all secure - checked them all about a dozen times.

I'll try loosening the TPS switch and do your test tomorrow Sox. The only things left that I can think of are the speed and ref sensors. When the engine has a brief spell of idling with the throttle closed, it runs like its experiencing a misfire every now and then and the tach jumps about 100 RPM. Then it dies. The engine revs up clean and smooth - after getting the revs up, the engine will idle briefly then go into the misfire mode then die.

Sucks not having datalogging - I haven't installed a WB kit on this car yet. I'm waiting on PLX's new R-800 which is going to be nice.

I know you checked them, but a WOT run then all the sudden it won't idle REALLY sounds like a hose got blown off. Check even those you can't easily see, like the hose from the bypass valve to the intake boot < --- I had mine blow off once, car wouldn't maintain an idle, but was drive able if I maintained higher revs when stopped.

Have you pressurized your intake track yet for leaks? It does sound like a cracked hose that leaks on vacuum. Any chance your idle adjust screw on the throttle body popped loose?

just food for thought i bew apart my turbo to intercooler hose 2 times first time it took me about a monther figure out what was wrong the second time i check it first and sure enough it was blowen. now that was with stock pipes. also you may want to make shure the screw is still in the top of the throttle body as i have heard that they do like to work them selves out from time to time ( i sealed mine in). also are you getting boost leak? if so then you know you have a hose off for shure. you may also want to go through the TPS adjustment procedure.

note i for got to say the symtoms of the blown apart hose is boost leaking and a poor idle untill you give it some gas then its fine.

Have you tried bypassing the ISV by jumpering ports B and C on the diagnostic socket and resetting the idle?

Ok, I just had exactly the same symptoms except i did not do any WOT runs. luckily i had the part that fixed my problem in my car. My car drove 36 miles no problem then when i got off the highway as soon as i pushed in my clutch the car died. and would crank but would not start. i could clutch start it and it would run great except it would not idle at all it would just die. i check all my hoses and connectors and what not nothing was wrong. I swapped out my DME relay out of chance that it may be it and blam my car started and ran. so you may want to check that and swap it out with a known good one. The one that was in my car was pretty new. But it still died. just a suggestion.

hey vic, have you actually tried testing all vac. lines using a hand pump? i've seen many instances where the connections seemed fine, but leaked.

Thanks for all the input guys. I haven't had a chance to work on the car again yet.

I will be pressurizing the intake track and checking for leaks - I thought it was a leak right from the start, but I haven't found one yet.

I've swapped a couple of DME relays already with no change. I've jumpered the B and C pins for the ISV and I've even changed it out with a known good one and no change.

It's raining here today, so it looks like I'm going to get wet playing with the 951. I'll post my test results once I'm done.

Pressurized the intake track and found that one injector wasn't fully seated into intake and one slightly loose clamp on a boost tube coupling. None of these fixed the problem.

Sox, with the TPS switch screws loose and switch rotated off the "click" the car idles stable at just over 1000 RPM. When I close the TPS switch with the throttle body at the idle position, the engine RPM drops and below 1000 RPM and engine begins to stumble occasionally then will die soon after.

When the engine is stumbling, I see the tach jump a hundred RPM - sometimes the engine will recover to idle speed but most of the time it won't and it'll stall.

"Sox, with the TPS switch screws loose and switch rotated off the "click" the car idles stable at just over 1000 RPM. When I close the TPS switch with the throttle body at the idle position, the engine RPM drops and below 1000 RPM and engine begins to stumble occasionally then will die soon after."

So if I understand right...
1) throttle is at idle.
2) the tps is rotated to make the car think that the throttle is off idle.
3) car idles steady at 1000 rpm.
Are the above statements correct ?
then...
1) throttle still at idle.
2) tps is turned back to normal (you hear the click) and the car thinks its at idle.
3) problem returns.
Are the these statements correct ?
also
"changed FPR, TPS, new fuel pump, replaced ISV, DME temp sensor, checked/cleaned cap and rotor and I'm at the point of pulling my hair out!!"
So all that stuff is new ? (plus new hair :) )?
Sox

You're reading it right.

All parts mentioned have been replaced with new or known good parts.

There are two ways to trouble shoot further, electrical or mechanical. It depends on your comfort level with either. If you can use a dvm and clip leads etc. we can do electrical if not we can do mechanical (the mechanical is more work intensive taking the isv off etc.) which way do you want to go.
Sox

I've already had the ISV off and replaced it with another unit - it's not a big deal to pull it off again. I'm fine with a DVM as well.

What do you suggest?

Ok here is what you do.
1) disconnect the hose that goes from the isv to the manifold (3rd nipple down).
2) disconnect the hose from the isv to the hard pipe just up stream of the throttle.
3) connect a flexible hose from the hard pipe to the nipple on the manifold.
4) find some way of pinching the the hose so you can control its opening.
5) start with it wide open and start the car. It should surge from 800 to 1600 rpm and back.
6) pinch the hose down and you should be able to control the idle and bring it to 800 or 900 and hold it pretty steady.
If the above works then (the isv is new) either the connection to the isv is bad or the dme has a problem.
If it does not work we will try something else.
Sox

Would your test with a DVM be a quicker test?

Yah you could disconnect the isv connector and use a 9 volt battery to jolt the isv back and forth to control the idle. If you can control it by this method then the same conclusion as above.
Sox

I'll try bypassing the ISV tomorrow and will post the results. The TPS switch should be hooked up as normal right?

I'm also going to try to ohm out the terminals on the ISV connector to the DME connector to see if I've got any opens.