I think I fixed my previous problem of a stumbly idle... I cleaned and reset the IAC, checked the TPS voltage, and replaced the oxygen sensor. I also adjusted my idle RPM to a comfortable level. Now, when I tap the gas while the car is idling, the throttle body makes an odd noise that sounds almost like it's gasping for air... very similar to the same sound that's made when you start a car without its air cleaner or TPI air bellows. If I gradually increase the gas it doesn't do it as much but it's still there. After about 2,000 RPM it's all gone. I don't know if the car makes this noise in Drive... I've been testing it out in Park. The plugs were replaced about 4,000 miles ago and the fuel filter was replaced about 5,000 miles ago.

Also, when I start my car, the RPMs increase to about 1750 and then over the next 10-15 seconds drop to my idle RPM of about 700. What's up with this?

 

Blow through a straw... I'll bet you get a similar "whoosh"... Totally normal...

An engine is a big pump... the more fuel and air it can consume, the more horsepower it can put out... your engine is just suckin in air...

 

You can't just turn the throttle plate screw to change your idle RPM. THere is a specific procedure for that. Idle RPM is controlled by the chip programming ONLY. Cranking up the idle speed manually and then adjusting the TPS to read correctly at the elevated RPM is a no-no.

Putting all that aside for a moment.....

If someone dropped a 350 into your car (which never could have come from the factory like that) it very well maybe that they have the wrong sized injectors in it. Had the EXACT same off-idld stumble in my brother's (much more modified) 87 GTA. We THOUGHT we had 30# injectors in it, just liek the chip we had burned called for. Nope. Somebody sent us the wrong injectors- only 24#. After drivin us buggy for months we ran the numbers on the injectors (in conjuction with spending a full day of Diacom scan time on it) and found out they were not what we thought they were. A set of 30# Accell injectors later and it was GONE. TOTALLY fixed. MAF systems are VERY sensitive to matching the injectors to the chip's programming (injector constant in particular).

 

Hmm, interesting... how hard are the injectors to remove just so I can check the numbers? Yesterday, I removed my throttle body and cleaned it. I also replaced the IAC valve and set the idle RPM according to Vader's instructions. The car seems like it's running pretty good now, but I'd really like to see if I have the wrong injectors. What size injector did the stock L98 350s come with?

 

I just checked the numbers on the injectors... 5235302, which came on 1987-1988 350 engines. So, I may have the correct injectors, but could they be so dirty that they would lose a few lb/hrs in flow rate? If this were the case, would there be more problems than I currently have?

It's a little odd, though. I haven't done any actual tests, but it seems like my car is running rich. Today I think I'll hook up a voltmeter to the oxygen sensor to find out for sure, but it just seems like my car has always been running rich -- I only get about 13 mpg, too. The richness that I may be experiencing could be because the guy who swapped in the 350 didn't put in an OEM 350 chip, he put in a crappy "ADS SuperChip" for a 350. Who knows what that thing did to the engine parameters. I've been wanting to put a stock '87-'89 MAF chip in there for a while but I don't have access to a chip burner.

 

Blue,

If you adjusted the throttle minimum air position according to the directions (with the IAC disconnected) and then reconnected everything as instructed, the ECM should be controlling the idle RPM.

The noise you are hearing is likely the IAC air that is now able to flow through the clean passages, but that is normally muffled pretty well by the intake bellows. Just to be certain, double check all the hose connections and routes. The reason the noise is gone at about 2,000 RPM is that the IAC is no longer effective and is essentially fully closed.

As for the rich condition, checking the O² is a good starting point, since that is the main device that the ECM is trying to satisfy by adjusting fuel rates.

Regarding your injectors, the part number and size may be right, but if they are dirty your flows can be reduced, and possibly more importantly, the spray patterns may not be acceptable. A good injector should atomize fuel in a parabolic "cone" pattern eminating from the tip. This provides the best fuel mixing with the least amount of liquid fuel consumed. An injector with a dirty or worn tip or clogging screen may spray a stream, drip, or develop droplets instead of a fine mist cone pattern. Unfortunately, the only way to see this is in a test fixture with the injector out of the intake.

If you suspect a bad injector, you can perform a power balance test of the injectors to help determine if any and which ones might be defective. If you're interested, I have a procedure. Since you've already done the IAC/TPS/Minimum Air adjustments, you already have the tools required and have done a very similar procedure.

 

Hmm, Vader's the man :hail:

Someday I'm gonna be as smart as him Then I'll be able to help alot of people and tell them how it is ;]

 

I second that . Vader, I'd like to see that procedure for the injectors. I'm assuming that it involves tapping off the wires that run to each injector to read a certain value?