I completely disassembled and cleaned the throttle body, it is spotless. Bought a new IAC and installed and set as per instructions. The TPS on a 91 Corvette is not adjustable. Starts and runs fine but after it is warmed up it idles around 1200 RPM. Checked everywhere for vacuum leaks and find none. It is the same as before doing all this work (and spending all this money) Any ideas?

Aloha,
Larry

 

Have you had a chance to hook up a vacuum gage? How about a FP gage?

If you are leaking a little too much fuel into the engine, the IAC will compensate somewhat to try to bring it down. Another thing to try would be to choke off the air into the engine (put a piece of cardboard over the air filter box). See what those things come out to and let us know. Timing could also be advanced too much...

The other thing to note is that after warm-up, the engine starts using the O2 readings. If there is a leak in the head to ex. manifold gasket flange of at the manifold to pipe connector, the O2 can 'functify' the mixutre. The O2 could also be getting lazy in which the signal could be off. If it has been 40000+ miles since your last O2 sensor, you might wanna pop one of those in just because. -Matt-

 

Fuel pressure gauge, yes 47#, vacuum gauge, no. Which one of the 107 vacuum hoses would I check? What would the cardboard over the air filter tell me? Wouldn't it just choke the engine until it stalled? Would the IAC let in enough air to compenste for blocking the air intake? The timing has never been touched in the two years I have owned the car (now with 35,000 miles). I did however go with the Hypertech ignition set up and cut back the spark plugs. Could that have anything to do with it? Thanks for all the help.

Aloha,
Larry

 

Larry, an old trick I have used in the past to find vacuum leaks is get a propane torch. Turn the gas on but do not light it. Wave it around all the vacuum hoses. When you go over a leak, your engine will injest propane and your idle will increase.

The other trick is to listen for a leak with either an automotive stethascope or just a rubber hose with one end cupped in your hand up to your ear and the other end running up and down all the vacuum hoses.

Again, if you would ever like me to come and help you, just send me a plane ticket. ;)

 

The others have said it already, but here it is again. To increase idle RPM, just add air.

If you can, use a scan tool to look at the IAC counts.

"107", there are very few vacuum hoses on the L98. 2 EGR, 2 PVCS, and 1 FPR. Ever look at an Asian car? :crazy:


[Modified by ZylaRace, 12:47 PM 10/3/2001]

 

You can use the same vacuum port that the FP regulator goes to.

Do you hear a mix of a whooshing or a whistle from the air filter area? If so, that would be your IAC going nearly to full open. -Matt-

 

High Hope 85,

At about 1900 RPMs I can hear a whistling sound in the area of the throttle body. It is the same RPM if I am accelerating or decelerating. So if that means my IAC is going to fully open what is that telling me? Thanks again to all of you for the help.

Aloha,
Larry

 

When my IAC went wide open, it was because I was dumping way too much fuel into the chambers. So here is what happened: Too much fuel, O2 sensor read high. Computer tried to shorten pulse width but I was still dumping too much fuel. Since it couldn't take out any fuel, it tried to raise the idle. Well, it did raise the idle, but since the IAC is a controlled vacuum leak, my vacuum which should have been about 16-17 in. was now about 5 in. In a nutshell, the IAC can be at any one of 150 or so positions. When you first start up the car, it is usually going to be around 50 counts so a high idle can be established. The IAC will then close to 0-20 counts, and this is when idle usually lowers. I would think the whistling/whooshing sound would be very pronounced if the IAC was going full open.

My problem? The pickup coil I purchased had the wrong polatiry, even though it had the right part number so my cylinders weren't firing when they should have, thus making the rich mixture. I know Dennis encountered a similar problem due to the location of the O2 bung in a set of long-tube headers. If you have an overly rich smell coming from the exhaust, I would start there. Otherwise, I am going to have to think a little bit more. -Matt-

 

How did your car run other than the idle problem? Mine runs very strong other than the idle.

Thanks again,

Aloha,
Larry