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Discussion Starter #1
HI, I'm new to the forum hoping someone can help with a problem thats making me crazy. My 91 2.5 starts and runs good until it warms up then idle goes sky hi. It first set 2 codes both for MAP sensor. I replaced the sensor, no joy. Since then no more codes but very high idle after warm up, about 2500 rpm. Replaced the IAC, nope not that. Replaced TPS, not that either. Checked for vacuum leaks, can't find any. Truck gets good mileage but does have a flat spot when shifting from 1st to 2nd. Also after warm up when idle is high I can unplug the MAP sensor and idle goes back to near normal, but truck is then undrivable with no throttle response at all. I'm baffled and about ready to take it to a real mechanic although I'd really like to fix it myself. Anybody out there have a clue? If so don't hold back give it to me.
Thanks in advance for any help.
Dave
 

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2 Litre Terror
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Sounds like an incorrect MAF. Did you buy it new or from a junkie?. After you installed it did you clear the codes...Comp. may still think it has the original MAF in it.
 

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Discussion Starter #3
Thanks for the quick reply. The MAP is new a Wells from autozone, and I did clear the codes. What makes me crazy is the belief that this is just something simple that I can't put my finger on, and also the fact that unplugging the MAP lowers the idle.
Again thanks
 

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2 Litre Terror
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The fact unplugging the MAF lowers your idle leads me to think that it's the problem. See if they'll exchange for you..Make sure there are not more than one for your truck.. Or go to the dealer..Have them look up the right part # and than use that to cross over at the auto parts store..Keep me posted..
 

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well the 2.5 didnt have a MAF it has a MAP setup. I would check to see if there is a restrictor or a one way valve in the vac line to the map that could be keeping it from getting constant readings... also check the ground wires on the block they could cause this also.
 

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Discussion Starter #6
02 Blazer
Just got back from parts store. As far as we can tell its the right MAP sensor and just to be sure they tested it for me. Works fine according to the chart. A guy in the store said that because it only happens after the engine warms up it might be the coolant temp sensor. In a way this makes some sense. Im learning that all these damn sensors are tied in together, and they all affect the fuel delivery system in one way or another. Now I have to come up with a way to check the coolant sensor. Again thanks for the response. I thought this might be a common 2.5 problem but it doesn't seem to be ringing any bells.
Take care
Dave
 

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Discussion Starter #7
Tha_boom, thanks for the suggestion I'll check the grounds. I've been all over the vacuum lines and can find nothing wrong there. Of course that doesn't mean its not a vacuum problem.
Dave
 

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My 1991 2.5 just started with the high idle problem. No trouble codes and check engine light works but does not go on when I unplug the IAC, which is my 1st suspect. Is this normal? I can't find any vacuum leaks. The truck starts very hard when cold and stutters and misses like it is lean so I suspect IAC is stuck or I have a vacuum leak in a casting or gasket that is not obvious. Did you ever solve you r fast idle problem and what was it?

Anyone else have this happen and solved the problem?
 

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im having kinda the same problem with my piece of shit but the idle on mines go real low instead wich sometimes makes it og off but when im driving down the freeway it all good its only when i make stops or slow down
 

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Float like a butterfly
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blazin low have you ever messed with the idle screw? ppl like to mess with it to change the idle which is the incorrect way to do it. sometimes theres a problem so they make it idle down and then the problem gets fixed and then the idles too low. also check the IAC for good operation
 

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nope never messed with it my problem started when i let a friend try my injector on his truck so he could see if that was his problem when he put it back it started fukin up, i think that ****er kept mine and put his on my truck
 

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check to make sure your IAC is tight, i cleaned mine and it pretty much sat at redline, went to take it out and noticed the bottom screw was only halfway in, such a tight fit it felt tight.

cranked them down and put a new engine belt on, idles just fine now
 
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