Idle problems

[clok1966]

Ok i have read the other threads, EGR or possilbey IAC, even the 2 relays behind the battery. But Before i throw money at it I thouhgt I would ask one last time here.

87, runs good most of the time. I have drove it about 30 X since i got it, and twice when i started it, it wont Idle. I dont think its temp related. It will just slowly idle down and die, whenver i stop at a light/stopsign, or if i shift to slowly whne slowing down. The strange thing is it seems to run fine several hours later (both times I have drove it home (cussing like a salior i might add) and it started and ran fine the next morning). It is possilbe it will run fine if it cools down, havent tested that. I am leaning away from temp problem since one time it happned when i was driving, and today it happned after i came out of movie, it had ran fine on drive there, we drove to movie, watched it and came out and it wouldnt idle. I have to keep my foot on gas to keep it running, it does run just fine as long as i apply some foot. Its just like an old Carb where the idle is turned to low, runs fine when you are useing the gas, but when your foot it off it it dies.

I'm leaning towards IAC, I know Junk says EGR (well he has mentioned it might be a good place to look, not that that is "for sure it" ), but if it was stuck with a piece of carbon (or whatever) I wouldnt think it would just disappear overnight. Also a question, how do you get to the EGR? Do you really take the runners off that cover it? WOW, seems like a pain to get too.

IAC- where the heck is it, is it right up front buy the MAF on the bottom of the tube sorta? I bought a IAC and did a quick look and that is where it appeared to be (engine was to hot to get a good look).

Any other suggestions? A manual is impossible to drive when it wont idle, and very very embarrising whne you die at every stop and have to restart it. it really spoiling my "fun".

Clok

opps dang it this should have been in Tech

 

[Toms007]

I'm not 100% sure on an 87, but the IAC on my 94 is on the throttle body, passenger side directly under the TPS (Throttle Position Sensor). Mine had 2 small screws holding it in (the bottom one a little more difficult to get to). I disconnected the the wires to the IAC and TPS to gain a littlte space to remove the IAC. If you have a new one, use a little Throttle body cleaner and clean the hole in the TB before installing the new one. I hope this helps you, and it fixes your problem.

 

[clok1966]

Thanks Tom, that is where it appeared to be when i looked also. I will make sure i post the solution when I find it (will take a few days to know since the car runs fine 99% of the time). I have noticed alot of the threads with problems have several solutions, and the original thread starter will post he solved the problem, but they never say what solved it

Clok

 

[LT4man]

Welcome to CAC!

Yes, you have to remove the plenum to get at the EGR. Not that difficult.

Junk always installs a piece of stainless steel screen between two EGR gaskets when he reinstalls them. Only stainless steel will not corrode from the exhaust. Screen breaks up the carbon into smaller pieces so you will never have this problem again.

The issue you are referring to is very common. The carbon is flying around and constantly gets stuck in the valve. Better to take care of it once and for good!

SAVE THE

 

[gmjunkie]

The IAC and TPS on a 87 L98 are basically in the same Locations as the LT1! (See Photo below!!)

1.There is a Temp sending unit just below the thermostat! I've replaced several because they were out of range after Warm up!!And caused the same symptoms you are explaining!!(May or may not throw a code!)Unfortunately you will need scanner that will read Real Time data to tell if it's that!! (See Photo Below on Location!)
2.Also on numerous occasion's I've found on L98's the 4 mounting bolts and the screws in the plate on top plate loose on the throttle body causing your same symptoms!!
3.Dirty IAC or Sticking IAC is purdy common!!
4.A faulty or out of range TPS could also cause similar problem,But I've never personally ran into it!!
5.Not as common,but I've also ran into a worn throttle shaft leaking air around it!!(Usually drivers side where the cable is attached!!

The 2 wires and plug below the hose are on the end of the temp sensor
way down below the throttle body!!

TPS is on the top and the IAC is on the bottom of Right side of throttle body!!

Make sure the 4 mounting bolts and 6 screws on plate are not loose!!

These are photos of a 87 L98!!

PS.I really don't think it's in the EGR,but it's possible!!You may want to check it!!
I've not had near as many EGR problems with the L98's as I've had with LT1's,4.3's and 86-94 305 and 350's in Pick Up Trucks!!

 

[clok1966]

WOW thanks Pics help alot, I have worked on alot of cars but to be totaly honest I havent been wrenching much in the last 10+ years (last car i worked on alot was crossfire Camero (84 I think, been so long ago?)) most of my work is with carbed stuff and this is all a little new to me. Throttle shaft, seems unlikely to me as it should run crappy a little more regular. It runs as perfect as can be, then wham, it wont idle. I bought the IAC and will replace that first (and check those bolts).. Temp sensor, i think that is ok as it will when idleing get to the point the fan will come on (226 i think) keep in mind its a 93-94 here and it has to idle awhile.. normaly cruiseing around im 180ish little warmer or cooler depending. But replaceing it may be my next step (asumming its cheap and not some "we only used it one year so its $$$$ part). I have a code reader (its not throwing any codes), but no real time equipment, have been thinking about getting some though, but to be honest the vette is the only OBDI car i own, so while not horribley expensive, it seems to be possibly more then I want to spend, but then again I think I will be hanging onto this car a long time.

Once again to everybody, THANKS! every $ i can save doing it myslef is a $ i can spend on new parts (my interior is kinda beat up).

Clok

 

[Toms007]

I have an AutoXray 6000, it will do OBDI and OBDII does real time monitoring (I admit to never having done it though) and not terribly expensive.

 

[gmjunkie]

There are 2 Temp sensors on the engine!! The one in the head between #6 and 8 cylinders controls the Cooling fans!! Try squirting WD-40 around the throttle shaft while it's running and you will find out if it's leaking real fast!!As far as that go's it will find a Vacuum leak in the throttle body too!!

 

[hdguy42]

There are 2 Temp sensors on the engine!! The one in the head between #6 and 8 cylinders controls the Cooling fans!! Try squirting WD-40 around the throttle shaft while it's running and you will find out if it's leaking real fast!!As far as that go's it will find a Vacuum leak in the throttle body too!!

GMJunkie......you are so right on two temp sensors. The one nestled above the water pump tells the ECM whether the engine is hot or cold, which hence adjust mixture accordingly. Replacing it help in many, many cases. On an 84 replace it with the updated version with two wires!

Nice work....GMJunkie!

 

[clok1966]

Wow that 87 engine looks as dirty as mine I replaced the IAC tongiht, my socket wouldnt fit on the thing so i had to pull the whole throttle body and use an Open end wrench. myabe a good thing, it was slightly sooty, i cleaned it so that cant be bad. The car idles different now, before it seemed to always idle at about 6-7 when i engaged clutch or was sitting at stop lights, sometime it would even drop to 4-5 ( not often). Now it idles at about 10 when I'm clutching, and if i sit at a light it drops to about 7 in 1-2 seconds. there is a change for sure, but if I fixed my problem only time will tell. To be honest it seems to Idle better, actually run better, but it may just be wishfull thinking and hopeing i have repaired my problem.

So if theis thread has no more for me, it was the IAC, if ther are more posts about the problem, well then its something else Once again thanks for the ideas/help!

Clok

 

[gmjunkie]

Wow that 87 engine looks as dirty as mine I replaced the IAC tongiht, my socket wouldnt fit on the thing so i had to pull the whole throttle body and use an Open end wrench. myabe a good thing, it was slightly sooty, i cleaned it so that cant be bad. The car idles different now, before it seemed to always idle at about 6-7 when i engaged clutch or was sitting at stop lights, sometime it would even drop to 4-5 ( not often). Now it idles at about 10 when I'm clutching, and if i sit at a light it drops to about 7 in 1-2 seconds. there is a change for sure, but if I fixed my problem only time will tell. To be honest it seems to Idle better, actually run better, but it may just be wishfull thinking and hopeing i have repaired my problem.

So if theis thread has no more for me, it was the IAC, if ther are more posts about the problem, well then its something else Once again thanks for the ideas/help!

Clok

Now disconnect the neg battery cable for 3-5 minutes,Reconnect and drive the car the ecm will reset all the perimeters and I think it will be A-OK after a couple start and warm up cycles,It won't take long!!

 

[clok1966]

Well it appers teh IAC fixed my idle problems, hasnt happend again in alot of driving (would be now but its raining hard). But I seem to have a new Idle problem. I did have the battery disconnected for the install, and its been disconnected again since. I'm idleing about 800 now instead of 700 (that doesnt bother me). But when Im driving the car in teh higher gears and more rpm's, say a shift from 3rd to 4th. My RPM is say, 1400, clutch in, the RPM wont drop.. with clutch in it just hangs wherever it was. Somebody said to jumper the diagnotic pins and remove battery or something like that? Anybody have some advice on that. It does idle down at stop lights and such, its just while driving the RPM doesnt seem to drop.

Clok