gasouthernxj

Hello CF!

So, my poor 1992 4.0 4x4 XJ has been having a hard time lately. I went to fill up a week ago, it was pretty low (18.5 gallons put in). After filling her up, i went and cranked and it seemed to stutter a little bit after turning over (kind of like a cough, it wasn't a backfire though), and the RPMs were really high (around 1,200). I've had this high RPM issue before but it someone went away (meaning my normal idle RPMs were about 900, which i've heard is actually still kind of high) for a couple weeks and has now returned. The only thing I have changed is the type of gas, I started using 93 octane ethanol free for a few weeks, and that's when the high RPM went away, I then started using Chevron regular 87 & mid 89, it still ran fine for those two fill ups. Then I went and put in Chevron 87 ethanol free, and that's when this all occurred.
Now, starting this week it has started having really long crank times (7 seconds or more) after sitting for a little bit. I tried cycling the key a few times just now and it cranked right up, I'm going to try again in the morning and see if it still works. My question is, would a bad fuel pump cause high RPMs too? It's not just a high idle, the RPMs stay proprtionally higher at all speeds.

Thanks in advance for any help!

Big David

My '88 MJ would do the high rev thing. One day I got under the hood & started tapping around with a pocket knife on the throttle body. The rev's went down. Every once & a while it would do this & the knife fixed it.

The long crank could be a leaky injector.

gasouthernxj

The injectors are actually brand new. And by "brand new" I mean reman.

So you literally would just take the knife and tap around on the TB? As in hit it lightly?

highmileage

Vac leaks, TPS out of adjustment could explain the high RPM. Long crank time could be a fuel pump check valve.

karl4x4

Its not uncommon that the air bypass valve on the throttle body gets a little dirty and lets more air in than it should. Hence tapping on the throttle body got it to seat properly and do its job. Good thing to do is get some throttle body cleaner (spray) and spray it. Chrysler has a good product that cleans your whole intake part of the engine. Good luck

gasouthernxj

thanks guys, I just replaced a pretty worn out vac fitting, no change in RPMs yet, but I'm assuming the ECU will take some time to re-calibrate IF what I did fixed it, right?
I'll check out the throttle body in the morning and also see how long it takes to crank.

gasouthernxj

It seemed to start right up this morning, I wonder if replacing that vac fitting (the one that connects to the intake manifold from the valve cover) had anything to do with it?
RPMs are still up, will be installing cleaned throttle body/sensors and new plugs this evening. Hopefully that will fix the high idle.



That's where my RPM sits while in park.

gasouthernxj

All right, TransAm79 and I just spent the last two hours installing new spark plugs and cleaning the IAC on my TB. We also reset the ECU. No change in high RPMs. The long crank seems to be gone, however.

I was under the impression that the TPS was not adjustable on a 1992?

TransAm79 said maybe the computer thinks the A/C is on all the time? His reasoning was that I turned my A/C to Max from off and there was no change in RPMs. Does that sound possible?

TransAm79

When we were looking at and listening to everything, it does idle smooth, just a tad bit higher than it should. It idles exactly where both of my XJ's idle with the A/C clicked on. I had him click his A/C on and not a sound, or a difference RPM's. That was my next guess...any input would be a good start. It's bothering me now...

gasouthernxj

I just pulled the A/C relay and fired it up, still high idle, so I doubt that's it. I'm at a loss.

gasouthernxj

Anyone?

cruiser54

Spray around your intake and vacuum fittings with throttle body cleaner at idle. When you hit the vacuum leak, you'll know it.

gasouthernxj

I've done that a couple times with brake cleaner, but I'll try again.

cruiser54

OK. Brake cleaner will work but keep in mind that anything that can potentially get sucked into the intake has to be oxygen sensor safe....

gasouthernxj

Does anyone have a vac line diagram for a 92? I must be missing one or two somewhere. I can't find any leaks.