Racing engine

I have a 2003 Jeep Grand Cherokee with 70k miles. The engine races when in park when it is started , going up to 1900 rpms or so. Sometimes it comes down below 1000 and sometimes it doesn’t. Sometimes it races up an down while being driven . Neither the dealer nor two mechanics could figure out what it is ; although one mechanic changed some part out , the name of which now escapes me , but it may have been some electronic part . The check engine light is on continually . Has anyone had that problem ?

Let’s see ,your engine is running poorly and your check engine light is on.The check engine light is there to tell you something is amiss. Get the code read at your mechanic, or if you want to fix it yourself , go to Autozone or one of the other auto parts stores that read the codes for free.

Thanks for your input. The mechanics have been ask to analyze the check engine light each time I have had it serviced. After one attempted repair , they were able to get it off ; however, it came back on within a day or two later . None of the attempted repairs had any effect upon the racing engine. ( Although one reputable mechanic admitted he had no clue as to the reason for the problem and consequently , did not charge me. ) Therefore, I can only conclude that whatever codes the mechanics have read do not offer a clue as to the racing problem , and apparently , the reason for the check engine light. Does this additional information give any more insight into the situation?

No. We still need the codes to understand the problem. The computer controls the idle speed, so the problem behind the check engine light may have a direct bearing on the idle speed problem. We just cannot say without knowing the code. Check a recent work order from the service done and see if the code or codes are on there. They will be in the form of Pxxxx. Otherwise, see if an Autozone, Pep Boys, O’Reilly’s, or other parts store in your area will read them free for you.

I believe you should be able to read the code yourself. It will appear on the odometer read out. Just cycle the key from off to on 3 times (ON:OFF:ON:OFF:LEAVE ON) DO NOT START. It should, if capable, show the code(s). If it’s multiple codes, hitting the reset stub will cycle to the next in order. If there are no other codes, it will read “done” in lower case graphics. This is the case with my 2002 Wrangler.

There are only a couple of items that can result in a variable rpm with no input from the throttle. Assuming that that AIS motor is moving freely, and there are no vacuum leaks that are within the range that the AIS can compensate for, it would probably be something like a TPS …but that doesn’t quite fit either.

In any event get the actual code and post it.

Try something (just for testing purposes). Disconnect the electrical connector to the idle air control valve (iacv). Start and run the engine. Drive the car for a short piece. Does the rpm stabilize; or, is there some other effect?