High RPM

[prerunner1982]

Lately I have noticed that sometimes my RPMs are higher than normal, in gear it idles at about 1k rpm. When I am going and let off the gas it almost has enough RPM to maintain speed. If I take it out of gear it still idles high, has poor throttle response, and when I tap the throttle the RPMs seem to take longer to come down. If I turn off the Jeep when the RPMs are high it is hard to start unless I let it sit for awhile so it seems it is running rich and flooding the engine when I turn it off.

Now here is the interesting part, I have also noticed lately that my temp gauge won't always work and it wasn't until tonight that I realized that when the temp gauge doesn't work the RPMs are high, when the gauge starts working the RPMs come down to where they are supposed to be (about 800 rpm at idle) and the throttle response returns.

Not quite sure where to start and why the temp gauge makes the idle kick up.

Any suggestions?

Thanks.

[nickyg]

Jeep was owned by AMC. AMC invented the Gremlin. A funny looking compact auto and also A little green man that eats 500 pounds of electrical wiring a day. What did you expect?
I suggest you exorcise the gremlin by shaking a chicken foot at your jeep and chanting "thank God it's not a renix"

[4.3LXJ]

After exorcizing gremlins, check for the vacuum leak they created

[prerunner1982]

I thought vacuum leak at first as well but the fact it's tied to the operational status of the temp gauge threw me a bit.

[4.3LXJ]

I was going on the idea it was a coincidence. I can't think of an association between the two

[prerunner1982]

Me neither but I have been paying close attention to it now and there is.... some how.

[4.3LXJ]

Full of antifreeze?, No air in the system?

[Cheromaniac]

Here's some things you could try:

Disconnect the negative battery terminal
Clean the inside of the throttle body
Clean the idle air bypass valve and barrel
Lubricate the throttle linkage
Check the wiring connector to the temp. gauge sending unit for looseness, clean contacts, and reconnect
Reconnect the battery and start the engine.

[prerunner1982]

I am thinking it's the temp sensor.

I turned on my Torq app and it showed the coolant temp as 64*. Jeep had been running for well over 30 mins so I knew it was up to temp. I believe the ECU is seeing the wrong temp and adding more fuel to try and get the engine up to operating temp. I was able to stop while it was messing up, pop the hood, and thump the temp sensor. The gauge read correctly (195.10*) and the RPM kicked down. I don't know if thumping it did anything or was coincidence (could be a loose connection).

So ECU seeing wrong temp and dumping more fuel into the engine... sound logical?

[abebehrmann]

Doesn't the computer boost the idle rpm until it warms up a bit? If there were a problem with the temperature sending unit making it read cold when it really wasn't, I would think the computer would see that and boost the idle until it reads warm which might explain all your symptoms.*

*Obviously everyone else who commented on here knows more about these things than I do so take this comment with a grain of salt.

[denverd1]

I am thinking it's the temp sensor.

I turned on my Torq app and it showed the coolant temp as 64*. Jeep had been running for well over 30 mins so I knew it was up to temp. I believe the ECU is seeing the wrong temp and adding more fuel to try and get the engine up to operating temp. I was able to stop while it was messing up, pop the hood, and thump the temp sensor. The gauge read correctly (195.10*) and the RPM kicked down. I don't know if thumping it did anything or was coincidence (could be a loose connection).

So ECU seeing wrong temp and dumping more fuel into the engine... sound logical?

sorta, except that cooler air (64*) is more dense with more 02 than hot air, so it should produce a lean condition. Also your IAT (idle air temp) controls the mixture, not engine temp.

I think you're on the right track though. your MAF sensor may be on its last leg, looks like they run rich when going out. Should throw a code for you but may not until its completely toasted. any CELs?

[prerunner1982]

any CELs?

Yes, but unrelated.

[prerunner1982]

Some guy named "Carves" posted this over on JF and I have quite a few other references with the same info. "Put a scan gauge in your vehicle and you can watch the OBDII system, loop change over at about 65'f."

[prerunner1982]

Also per the Snap on Diagnostics Chrysler and Jeep parameters/

[prerunner1982]

Going to check connection at sensor and replace sensor if needed.