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Same High Rpms When Starting

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Hello. I've been having this issue for a while. Sometimes when I start my truck, the RPMs go to 3000 until I shut the engine off. I just cleaned my throttle body and readjusted the TPS. Replaced most of my vacuum lines.  Can't figure out what else it could be.  

 

Thanks. 

 

I have an 88 4.0. 

 

EDIT: Forgot to mention it does have a new IAC and MAP and it happens when cold or hot. 

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I endured intermittent high rev's on start up. One of the relays near the battery is supposed to allow the IAC to reset after you shut the engine off. Recommend cleaning the contacts and you can also swap the relays around.

 

My problem was cured after I cleaned the connector for the coolant temp sensor.....and I also replaced the ECU at the same time with one from a 1990 Cherokee. So I can't be sure which one solved it. But I cleaned a lot of things first, so please don't run out and simply replace parts first. Refer to Cruisers Tips for many cleaning things to do for Renix trucks. The C101 cleaning is a pain, but necessary along with grounds refreshing/improvements.

 

It is worthwhile to remove and clean the Idle Air Temperature Sensor located on the intake manifold. They can get pretty nasty over the years. I used electrical contact cleaner, de-greaser, and pipe cleaners. If the thermistor is covered with gunk, I'm not sure how it can get a good reading.

 

Recommend to start with cleaning things first, especially connectors.

 

Attached is the Renix fuel injection manual. It is a good read if you don't have it.

 

Are you still having stalling issues?

Jeep_Renix_Fuel_Injection_manual.pdf

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1 minute ago, SVPete said:

I endured intermittent high rev's on start up. One of the relays near the battery is supposed to allow the IAC to reset after you shut the engine off. Recommend cleaning the contacts and you can also swap the relays around.

 

My problem was cured after I cleaned the connector for the coolant temp sensor.....and I also replaced the ECU at the same time with one from a 1990 Cherokee. So I can't be sure which one solved it. But I cleaned a lot of things first, so please don't run out and simply replace parts first. Refer to Cruisers Tips for many cleaning things to do for Renix trucks. The C101 cleaning is a pain, but necessary along with grounds refreshing/improvements.

 

It is worthwhile to remove and clean the Idle Air Temperature Sensor located on the intake manifold. They can get pretty nasty over the years. I used electrical contact cleaner, de-greaser, and pipe cleaners. If the thermistor is covered with gunk, I'm not sure how it can get a good reading.

 

Recommend to start with cleaning things first, especially connectors.

 

Attached is the Renix fuel injection manual. It is a good read if you don't have it.

 

Are you still having stalling issues?

Jeep_Renix_Fuel_Injection_manual.pdf

1

 

Thanks!

So far, I have removed the C101 and gotten a newer ECU too.  

My stalling issues have gone away. I think it was a bad O2 sensor that was causing it. Idle improved too. 

 

I'll get to cleaning today and see where it gets me. 

Thanks for the tips.

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The throttle cable on the '88s doesn't run from the peddle to the throttle body. The cable connects to a lever (I believe the correct term is "bellcrank") on the lower driver's side frame "ear," down beneath the master cylinder. The other arm of the bellcrank pushes a lever that, in turn, activates the throttle body. The bellcrank rotates on a hinge/knuckle joint. That can get rusty and/or cruddy. Find it, and spray it down with PB Blaster and see if that helps.

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2 hours ago, Eagle said:

The throttle cable on the '88s doesn't run from the peddle to the throttle body. The cable connects to a lever (I believe the correct term is "bellcrank") on the lower driver's side frame "ear," down beneath the master cylinder. The other arm of the bellcrank pushes a lever that, in turn, activates the throttle body. The bellcrank rotates on a hinge/knuckle joint. That can get rusty and/or cruddy. Find it, and spray it down with PB Blaster and see if that helps.

 

Oh nice. I'll check it out. 

 

Thanks!

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