hey all,

my 99 XJ (stock) has an intermittent rough idle. The P0171 code is persistent but it's my only code. When it's idling rough, fuel trim jumps to 32% but when accelerating or operating normally the fuel trim behaves normally (bouncing between +/-) The O2 sensors appear to behave normally as well. Has a recent MAF, TPS, and ECT, cleaned the IAC. Haven't found any vacuum leaks. If I switch between mid grade and low grade the symptoms are temporarily mitigated but the code doesn't go away. All 6 injectors tested at 14.0..

oh, when coming to a stop the rpm often drops to 300 and stutters before resuming a rough 750 idle.. light acceleration will cause hesitation. poor mpg is experienced as well.

any thoughts? appreciate the help

 

How do you replace the MAF on a Cherokee?

Part of the problem could be a lazy IAC motor, cleaning them is only temporary at best.

 

MAF sensor? unhook the wires and then unbolt using a T20 bit if I recall.. same process as IAC and TPS. MAF cannot be cleaned though..

I suppose I am looking for how to test the IAC before I drop $70 on a new IAC

 

MAP**

 

Also want to note that (in neutral) when accelerating to say, 3000 RPM, and letting off gas the engine slowly drops speed until maybe 2000RPM then quickly drops speed to idle.

oh, did a fuel pressure check and PSI went to around 50 but it couldn't hold the fuel pressure for any length of time

Anybody?

 

You mean the fuel pressure drops to zero after shutting the engine off? Two things can cause that. A leaking injector, or a bad check valve in the pump. Pull the dipstick and see if the oil smells like gas, if it does it's a indication of a injector(s) leaking after shutdown.

 

Since you've replace those other air/fuel parts, I'd replace the IAC motor too. I just did the clean thing as mine would not stay running at idle...that fixed it, but it was still running a little rough. Put a new IAC motor in, it's smoother at idle AND I've noticed improved acceleration. Seems the old one wasn't adjusting fast or far enough.

 

I havent started the jeep yet but was wondering if this might be my ground lol

I had been trying to find the ground where it might rub something. Never thought to pull the harness out into the light. Between 55 hrs weeks and a torn rotator cuff I didn't really like getting into it from the bottom..



The insulation pulled back from heat I guess?




Wrapped the wires individually with electrical tape and then as a bunch. Rerouted to the location seen here. Think it'll be safe there and less likely to rub on the Intake manifold.

 

Havent smelled gas in the oil but hadnt really checked. A leaky injector would show up when you put the voltmeter to it, right?

I'd guess the pump probably needs changed. Got 140k on it right now..