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Unread 12-24-2009, 04:10 PM   #1
Willy36
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1990 XJ Cherokee 
 
Join Date: Dec 2007
Location: FoCo, Colorado
Posts: 1,167
idle issue still

I had already started a thread related to this but misjudged what the cause was at that point.

Recently I've been having an issue where the first one or two times I come to a stop when the engine's cold, the idle will drop down to like 300 RPM and sound like it's going to die, but it always comes back up to normal every time. By the third or fourth time I come to a stop this doesn't happen even when the engine is still very cold (below the 100 mark). At the same time an issue started where before the engine would come up to 210, it would lack serious power and hesitate. I cleaned the hell out of the TB and now the power issue went away, but the idle issue is still there. Here's what I know for sure:
1. TB, including IAC, can not possibly be any cleaner than it is.
2. TPS, Coolant Temp Sensor, CKP are all good.
3. Air filter is very clean
4. Entire ignition system checks out visually and was just replaced about a year and a half ago (maybe 10,000 miles ago)
5. Fuel system has pressure and the fuel filter is less than 6 months old.
6. From what I can tell without taking the rocker cover off, the valvetrain (at least what can be seen through the oil fill hole) is very clean.
7. The MAP sensor reads 3.55 volts when it's supposed to read 4-5 but I think this may be because I'm currently at 7500 feet elevation so the air's a bit thin.

Before I go throwing any more money that I don't really have at it, can someone give me some good suggestions on what to check?

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Unread 12-24-2009, 04:29 PM   #2
tjwalker
It's the crank sensor!
 
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Brainstorming here....how about EGR? I believe your 1990 has this.

You shouldn't have egr function at idle if I remember right; it's been a while since I worked on one of those. But I remember them being susceptible to carbon build up which could leave the valve on when it should be off. And they can cause idle issues.

Renix guys, please chime in!
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Unread 12-24-2009, 04:54 PM   #3
maddzz
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Have you tried adjusting the IAC? You could also have damaged the pintle (I think what you call it) on the IAC when you cleaned it.
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Unread 12-24-2009, 11:02 PM   #4
Willy36
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Quote:
Originally Posted by tjwalker View Post
Brainstorming here....how about EGR? I believe your 1990 has this.

You shouldn't have egr function at idle if I remember right; it's been a while since I worked on one of those. But I remember them being susceptible to carbon build up which could leave the valve on when it should be off. And they can cause idle issues.

Renix guys, please chime in!
Ooh hadn't thought of that. I'll be sure to check that tomorrow if I get a chance. Thanks

Quote:
Originally Posted by maddzz View Post
Have you tried adjusting the IAC? You could also have damaged the pintle (I think what you call it) on the IAC when you cleaned it.
I was unaware the IAC was adjustable, could you please tell me how to do that?
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Unread 12-25-2009, 06:28 AM   #5
tjwalker
It's the crank sensor!
 
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Quote:
Originally Posted by Willy36 View Post
I was unaware the IAC was adjustable, could you please tell me how to do that?
Idle air control is not adjustable.
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Unread 12-26-2009, 04:07 PM   #6
Willy36
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Ok should be 2nd to last update on this issue for anyone else who may experience this problem:

After messing with and taking off and inspecting the EGR valve, I can almost 100% for sure say this is the problem. It sticks, but only just slightly and only when cold. This would seem to explain my symptoms perfectly. When the new one comes in in a week, I'll post up for sure.

tjwalker, thanks a ton for all your help
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Unread 12-27-2009, 05:49 AM   #7
tjwalker
It's the crank sensor!
 
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1999 XJ Cherokee 
 
Join Date: Nov 2007
Location: Central Minnesota, MN
Posts: 8,446
Glad I could help.

Be sure to let us know if the new EGR valve completely cleans up your symptoms.
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Unread 01-03-2010, 12:35 PM   #8
Willy36
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Final update: New EGR valve is finally on and all the issues have cleared up

Made my mileage go up a tad too.
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Unread 01-03-2010, 12:47 PM   #9
99Greenmachine
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JF is on a roll with getting solutions to the problems today
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