So, I got an 88 4.0 auto and for some reason the idle will fluxuate a lot. It will idle around 900-1000 rpms for a minute then it will drop down to like 400 then jump back up to 6-700 rpms and back down to 400 and up again then down then up and it will soon smooth out to 900 again for a minute, then it'll do it again. And when I put it in gear it will ALMOST stall but I can't get it to stall. Please help it's my dd and I can't have it breaking down on me! I just put my old injectors back in (their all functional) because my other injectors were giving me **** gas milage. Could that be it?

 

Was it doing it before you swapped back to your old injectors? If not, that should be an indication right there of what you did wrong. Retrace all your steps and make sure all vacuum lines, etc are hooked up correctly.

 

Well the problem is that idk if it was doing it before because I havnt been driving it, my mom has and she doesn't pay attention to that kinda stuff. And yes all the vacuum lines are all hooked up correctly and there are no vacuum leaks.

 

What I would do next is run some sort of fuel treatment product through the gas tank (I use Seafoam), to try and internally clean the injectors.

Then I would disconnect the throttle body, take it out, and clean it with some throttle body cleaner till it looks good as new.

While you have it off, take off the Idle Air Control Valve and spray it with carb cleaner and scrub it with an old toothbrush.

Then put it all back together with a new throttle body gasket. All in all should take you maybe 45 minutes.

 

I just cleaned the t-body about 3 weeks ago, and Ive ran a can of seafoam through the injectors when I first got her about a year ago but I guess another can won't hurt.

 

Well that was when the different injectors were in right? It wouldn't hurt. And you should do it a little more often than once a year.

 

I cleaned the throttle body when I had the last set of injectors. But I ran the seafoam through the factory injectors (the injectors I just put back in)

 

Oh okay gotcha. Hmmm well did you clean the IAC when you cleaned the TB? A fluctuating idle like that kinda screams vacuum leak though

 

Cleaned iac, re adjusted tps, ect. Ect. I would think a vac leak to but my shops osilascope shows no vac leaks. I'm perplexed:/

 

Have you developed any exhaust leaks down the line? Like a crack in your exhaust manifold?

 

I got even extra bad "knocken around" mileage when I went to 703's because my 02 sensor was shot. The 703's have a higher flow rate then the stock 18.6 lbs/hr, and with the 02 not working I only got like 11 MPG one tank. Getten more like 16 now with only short trips..I'm looking forward to a highway trip...someday!


https://www.cherokeeforum.com/f2/ren...ce-rms-133153/

 

Jealous!

 

Ha! Well, I'll be jealous of you next time I'm high centered on a stump or something.

 

LO freakin' Ling.

Could this possibly be his TPS? I've read (from Cruiser, of course) that it's a good idea to re-adjust the TPS after cleaning the throttle body. At least I think I recall reading that... it's late.

 

Definitely a good idea to check the TPS on the flat 3 wire connector per my instructions.

That said, the OP's problem could very well be caused by a bad 02 sensor.