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Low idle on startup


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This has been a minor issue. This is on an 89 MJ 4.0 5 speed.

 

When i first start her up...it start fine...the after a few seconds the idle will drop low..around 500 or so. It will not stall out...almost..but not wuite.

 

Let it sit and idle for 3-5 minutes and the idle will come back up to around 900 or so and be fine.

 

Let it sit and cool for 5-10 minutes..or longer and it will do the same thing.

 

I know the IAC is good (replaced it) the MAP is fine...no vacuum leaks ( which should cause it idle high usually anyway). I did check the TPS sensor and adjusted it...did not make much of a difference at all.

A

ANy ideas? It is not a huge problem I would just like to finger it out.

scott

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One thought is the EGR valve might be on it's way out :hmm:

 

A plugged / shot EGR will choke the engine right out, cold or warm. It seams that your having a problem with the cold engine, while the ECU is in 'open' loop. It could also be the O2 sensor causing your problem.

 

Try the EGR valve first, just unplug the vacuum line going to it, and plug the line, see it that makes any difference with how it runs cold.

 

If no change, then change out the O2 sensor. or even change / swap out the O2 pre-heater relay, 2nd relay on the right shack tower.

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Coll..I was thinking along the same lines....O2 was my first choice..but I also was looking at the EGR...but was not sure how to test it.

I will unplug the line and plug it up and see what happens.

The O2 I will replace if I have to...little buggers ain't cheap:-)

scott

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One thought is the EGR valve might be on it's way out :hmm:

 

A plugged / shot EGR will choke the engine right out, cold or warm. It seams that your having a problem with the cold engine, while the ECU is in 'open' loop. It could also be the O2 sensor causing your problem.

 

Try the EGR valve first, just unplug the vacuum line going to it, and plug the line, see it that makes any difference with how it runs cold.

 

If no change, then change out the O2 sensor. or even change / swap out the O2 pre-heater relay, 2nd relay on the right shack tower.

 

 

For answers sake, I posted with the same issue a few weeks back. Mine was a fubar'd EGR valve.

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