Question about 1991 Chevrolet Caprice
It's very common for these engines to develop a vacuum leak around the base of the throttle body. You can check for this with a stethoscope or a can of aerosol carb cleaner. Also, IAC valves are a common problem, but easy to clean before you replace it. Remove it and use the carb cleaner and a brush to remove the build up, also the crud inside the IAC orifice. Next clean the throttle butterfly valve and throttle bore thoroughly with carb cleaner. If this doesn't help, remove the egr valve and try and poor a little paint thinner through it when you're holding it upside down, it may weep a little through the pintle but it should not obviously allow the paint thinner to flow through. If all of this fails to help, you'll have to get your hands on a scan tool and read IAC counts at idle to see what the computer is trying to do. If the counts are high...above 50, the computer is trying harder to open the IAC to keep the engine running because of some kind of problem, usually mechanical. If the counts are very low...below 5, the the computer may be trying to counter a vacuum leak that is providing most of the idle air, which is unstable and can cause the stall.
Hope this helps.
Posted on Jun 21, 2010
Testimonial: "I added more comments for the first poster but maybe you can put your second though also. I checked the EGR and took it off for a closer inspection, also took out the IAC cleaned it with rag with some solution and brushed it. My question is, how far out should the needle be or how can I tell when the IAC is warn out. thanks ."
Like you said it could be the TPS, but is it an auto or manual,, If its a manual I would be suggesting the TPS,, If its an auto I would look at the kick down cable
Posted on Jun 21, 2010
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Posted on Jan 02, 2017
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