I've got a '89 tpi iroc with low kms, the problem is at idle the rpms rev up then down to almost a stall continusly. All ignition components have been up graded, fuel filter replaced and k + n filters installed. Car has no codes and seems to run not too bad off idle, has slight stumble at steady cruising speeds at times. hopefully theres enough info here, looking forward for any suggestions, thanks.

 

Welcome to the forum!
what your car is doing is called "hunting" first thing to check would be your IAC

 

I would also check the ohm readings on the injectors. They should be somewhere between 14 and 16. And check that all vacuum lines are intact and in good condition.

 

Sounds like the IAC ( Idle Air Control valve) could be dirty and need to be cleaned like mentioned above or what I think it is is that there is a vacuum leak somewhere.

If you have some,spray some brake clean or WD-40 around all the vacuum lines (there are a bunch) and if the idle goes up/cleans up youve found it (or one).

Try the IAC first...its the big circle thing on the left side of the throttle body (looking right at it). You'll need a pretty big wrench,like 1-1/8 or so to get it off and use some electrical sensor safe cleaner on the cone shaped part that goes into the T/B.

 

My LT1 did the same thing, checked everything, turned out to be the opti vac line was lose at the opti and created a leak. I know you don't have an opti but my point is check all vac lines carefully, make sure they are tight at both ends. cured my eratic idle instantly.

 

I checked out the resistance on my injectors and found that 4 are 4-8 ohms and
the other 4 are around 16 ohms. I'm thinking that I have a problem with a few injectors. I was thinking about getting aftermarket accel injectors but there are a few different ones I can get, the only difference I see is the lbs they put out?
What did the factory injectors put out? and can I put bigger ones in?

 

Not to hijack this thread, but I have a very similar post in the LT1 tech section. Is this common to occur also after running for a while when it previously did not stumble and hunt for correct idle or do you know? Thanks, and if you get a chance, check out my post as it is similar in problem (I think anyways) and is also a speed density car.

 

Its hard to remember this long ago,but I think the 305 TPI's had 26 or 28 lb injectors and the L98's had 32 lb .

 

305 TPI- 19#

350 L98 - 22#

Later