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Hey all, new xj owner here.
Just replaced head gasket, injectors, plugs. Jeep starts right up but is very choppy from 400-1500 rpm. It wants to idle low. Computer has been reset. Has great throttle response. After a throttle snap, the engine will bog down to about 250-400 then bounce back to almost 750 (warm or cold).

I'm thinking the IAC might be the culprit??? Or maybe another sensor??? I feel like i'm chasing my tail here. Bout ready to just get a whole new engine.

No codes yet...will have them read tonight.

Think I hit all the key points. Thanks for replies.

Tim

 

Pull the IAC and clean it with carb cleaner..You may wanna replace it...they are reasonable..I had some crazy idle problems...when I cleaned mine it calmed it down.

 

x2 with the IAC, it can't hurt. Though, I would have the battery load tested as well. I had a similar issue, but I would sometimes stall if the rpm bounced down too quick.

 

Fsher21... when you had the 'bad' battery, was it a rough idle and smoothed out at higher rpm?

I cleaned the IAC today... no difference.. waiting to read codes tonight.....

Thanks for the brainstorming. Any other IDEAS??

 

Yeah when it was getting any throttle at all, it ran fine, but as soon as I let off the gas, the rpm would drop down to like 400-500rpm and bounce back up to just under 1,000. It sounded really bad and everything would dim, and if it didn't bounce back up, it would stall.

I had the issue because I drive a quarter mile to work daily and that wasnt allowing the marginal battery to charge, and eventually even a long drive wouldn't help keep it charged. Also, if i shut it off and tried to start it again, there was enough juice to turn it over, but not enough to start it.

I just drove with 2 pedals and dropped to neutral at stops so i could keep the rpm up, and had the battery tested at autozone. All that just over an old battery lol

 

Battery wasn't is. Taking coil pack and plugs out, again.

 

Damn, the load test passed? Guess that is good but still don't have an answer.

 

Used a diff battery that is much newer. Just ran codes and all that came up was the tsp sensor p0122. Going to replace it tonight. Just doesn't seem like that would cause it to run rough. Keep all posted.

 

That was going to be my suggestion. I just replaced mine today with the IAC...I don't think this thing has ever run so well.

 

Culprit is .................................................. ...
A cracked head between 3 and 4. Gonna pick up a new head tomorrow.. Hope nothing else is wrong.