I have an '89 Iroc, with the 5.7. Its pretty much stock, but i have SVO 24 pound injectors, and a chip programed for the differnce. The problem is my idle. With my last camaro, when i started the engine from cold it would idle high for a bit till it warmed up and settle at an idle. With this car, at start up it surges up and down. When it warms up, it trys to stay at a normal idle, and holds one for a few seconds but has a tendency to stumble. For example, i'm sitting at a light... listing to the engine idle... idle idle idle idle.... stumble.... idle idle idle idle idle idle ..... stumble. Some times it seems like its going to cut out when i let my foot off the gas but catches. The problem gets worse when it rains sometimes... but goes back to normal when it gets warm. Normal being the sometimes stumbling. The car has good power, and i've done a full tuneup with no change. The fuel pump is new, and holds pressure. I'm just stumpped. My only thinking is a possibly bad sensor or something.

Any help, or idea where to start looking would be appriciated.

Joker

 

My car does the EXACT same thing... I cant really say if it was after doing my tuneup or not, because I did the tune-up the morning after I got my car, so I didnt really get to do much traffic with it....

I was going to clean off my TPS though, I have a feeling it might be a culprit.

 

What was included in the tune-up?

 

Maybe a dirty injector / partically clogged, not atomizing fuel very good. Try unplugging them one at a time to see if you can isolate that way.

 

Tune up was:

New 8.8 mm wires.
Spark Plugs (Bosch single plat)
Cap
Rotor
PCV
Fuel Filter
Oil Change
Cleaned the air filters (K&N)
Checked the timing. (set at factory)

Also, i checked the TPS, voltage was fine.
I took off my Throttle body and cleaned the carbon out of the air passages to the IAC.

I really don't think it is the injectors. I originaly changed them because two of the old mult-techs were bad and would give me a no start. When i changed them for the SVO's (less then 2 years ago) i also put in the adjustable fuel pressure reg and had a chip burned for the extra lb's. I of course tested them with the DMM before i put them in.... no point in putting in bad injectors.

I keep thinking its a sensor of some sort... i just can't imagine why the car doesn't go through the entire warm up cycle.

 

Sounds like you checked the most obvious, you don't say anything about the EGR valve/solenoid....maybe??

 

Changed both of them to get past Emissions back in August.

 

Lots of guys complain about those platinum plugs, might be a thought?

 

I'm about to the point where i think i'll just start replacing all the sensors and what not. Damn thing has like 148,000 on it... i'm sure they have seen better days. I just hope that maybe i'll see some changes. Figure i'll start with the cheapest and just work up from there.

Hopefully if i get this other job i'm shooting for, i'll be able to get some more money together to get some body work done and a engine rebuild while i'm at it.

eh.

 

Bob may have a good suggestion. A power balance test of the injectors might be revealing. 148K miles is a lot on injectors, even good ones. The chance of a streamer or partially clogged injector is relatively high.

 

Cant he just poor injector cleaner in the gas tank? or should he really take out the injectors and get in there?

 

maybe i'm misinformed, but i believe that injector cleaner really isnt the best permanent solution. It will get out a bit of it, but the problem will still be there, just to a lesser degree.

my car does the exact same thing, and it occured after i did a tune-up (and i did almost everything that he did in his tune-up, plus got a new catalytic converter... was trying to pass emissions thus the tune-up )

so right now i'm remaining hopeful that he'll find out what it is, and it'll be something that I can do to my car to get fixed finally hehe.

 

I'd try some regular AC plugs first and see what happens. From my experience (working at a parts store) people with almost any american engine (GM, ford, etc) seem to have problems with the exotic-metal spark plugs like those platinums. Oddly, I've never heard of any imports having problems with them.

I'd try the plugs first though. Its a cheap thing to try.

 

Actually, you might have missed it but i've already changed all the Injectors out. Originally, i had a no start problem coming from 2 bad injectors, and i replaced them all with brand New SVO 24# injectors and had my chip changed to compensate for the difference.

I had the problem (plus the no start when warm) before i did the injectors, and after changing them i wound up with just the crazy idle (but now it starts all the time).

Maybe i'll head out to the parts stores and just pick up a set of autolites and see if that does me any good. I hate the copper plugs because the points on the plugs always seem to wear so quickly. Granted you can just file them back up, but who wants to pull spark plugs ever other week. BAH