1988 hesitation

[Danwa]

I have a 1988 cherokee. It will, once warmed up stall when you just barely push down on accelerator. It stumbles then dies. It will start up again after it quits. I just replaced the fuel filter and checked fuel pressure, 31 psi. After these checks, same problem. Any thoughts would be greatly appreciated.

[martin]

You may be overdue for a thorttle body cleaning. To do a through cleaning it will have to be removed from the intake. I had my cleaned at the dealer and the tech hooked up the test set to make sure all the sensors are working.

If you have a garage you trust with the test set or a dealer mechanic who was there in 1988 when your XJ was new go to him. Tell them about your stumble problem let him figure it out. It usually an hour of labor to diagnose a problem.

You may have a vacuum problm or a bad EGR, so paying the professional would be good money spent.

[harrym]

You might check the Throttle Position Sensor (TPS). With the connector, connected, push a stiff wire in D - Ground and one in A - V+. Turn the ignition ON, but not to start. You should get close to 5V. Then move the wire from A to B. This reading should be about 80% of the voltage you had when connected to A & D. Loosen the 2 screws on the TPS and move the TPS for the adjustment.

[Skwerly]

Sometimes mine will rev upwards to 3 grand at startup, and i have to shut her down and keep restarting in order for it to idle lower, and then it goes to about 300 RPM lol. Classic TPS symptoms, i'm about to check mine out too, but i already have one on order. Anyone else ever experience the "screaming idle" symptom from a faulty tps?

[ptf18]

The idle on my "88 (owned since new) will occasionally goe up on its own. Being a 5 speed I dont notice untill ....for instance...I come to a stop light. I put the clutch in and rarooommmmmmm the idle speed goes up to...2k..maybe higher (no tach)and stays there.

Next time I drive it (coming home from worK) NO PROBLEMS...

Any ideas?

[88xjchief]

My 88 does the same thing. The tps is good. My o2 is bad and I am replacing it tommarow.

[woodywagon]

Was just messing with my 87 last night had high rev iusse, the black sleeve on the iac plunger ic catching going to try 1 out of another throttle body I have.

[Daddycajun117]

Mine does that in the morning. Noticed a few old vacuum lines. replaced them and hasn't happened since.

[8Mud]

It may be a combination of things, like low voltage to the IAC and the IAC sticking.
When I have high idle, I remove the IAC and squirt a little oil behind the piston into the piston gear rod and motor drive area. Don't try to pull the piston out, the far enough point is hard to judge and too far point will launch the piston and spring. You may never get it back together again without stripping the gear teeth. Be careful to get the "O" ring gasket back in straight and seated properly.
The symptoms will often disappear for weeks or if I'm lucky months. The high idle thing also seems to be temperature sensitive. Mine seems worse when the motor is hot or the weather is really cold.
Also noticed, after the motor has been running for awhile and the alternator has mostly filled the battery back up and the charging voltage comes down a little, I'm more likely to have high idle. Either the typical hot start high idle or the constant high idle (the 12-1300 RPM variety).
I do believe there is more than one thing going on, many of the high idle conditions, while related, are different problems that can happen alone or in tandem. The low voltage, sticky piston and temperature may all cause problems, together or separately.
I disassembled an IAC, to see what makes it tick. It was an original from 87. First thing I noticed was the grease or lube they used on the piston rod and motor gear was really thick almost puddy.

[Skwerly]

I checked out the vacuum stuff closely, found one completely off, but that's it. there is a vacuum line going to a canister coming off the exhaust manifold, looks kinda like an old school choke. i disabled that and the thing seemed to do great, but coulda been a fluke, sometimes it'll do that. I sure hope replacing the TPS helps since i have one on order and it was over 100 bucks lol.

[Wallyman]

My 1989 did that with every warm up....turned out to be the crankshaft position sensor. found that out at the dealership. its on the back of the head..actually its in the block...behind the engine above the bellhousing...

[Skwerly]

Man, by the time i'm done i could replace every single sensor and vacuum line on the Jeep haha. Ugh...... Hopefully that TPS does the trick..... fingers crossed.

[Skwerly]

It's weird, it idles extremely low, and if i set the idle up manually using the set screw, it'll go back down within a minute or two. Until, that is, it decides to actually read what it is set at, and jump to 2500 RPM the next time i start it lol.