JerrytheJeep

89 sport 140k. Has an issue when its just starting up where if I let off the throttle the rpms dip a bit, I don't have a tachometer so I can't say how much. More recently it won't dip as much, but ill be coming to a stop and it will cut out. Issue goes away of I drive for a few minutes though. I'm thinking fuel pump or filter, ill see if I can vet a Guatemala so I can measure pressure at the rail. Anyone know off the top of their head what pressure the renix system ran on? I recently replaced my dizzy with a junkyard part, and yes it is clocked correctly. Other than that, the motor is stock.

cruiser54

Ever clean your throttle body and IAC?

Make sure your intake manifold bolts haven't loosened up?

Courtesy of TJWalker:

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The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to)

"Gently" wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled

JerrytheJeep

I tried cleaning my iac a while ago, I think I only had carb cleaner though. Ill grab a can of throttle body cleaner and get to work. Ill also check my manifold bolts. If problems persist what might be the next step? I followed your write up and cleaned my grounds, I have yet to do the interior grounds though. I also put dielectric grease on all my connections, but I hear that can be bad as well as it blocks the connection?

highmileage

MAP sensor going out can cause the RPM dip, or a weak vac to it. The fuel pressure should be around 35lb with the regulator hooked up and 40ish unhooked.

cruiser54

31 with vac. 39 without vac.

cruiser54

Yes. Ox-Gard is preferable for the connectors. OSH should have it. I used to live in SJ BTW.

JerrytheJeep

I don't recall the brand I used, it was in a little silver tube though. I believe we've had this discussion before, you said Willow glen, Alum Rock area right?

cruiser54

Yep.

JerrytheJeep

Wouldn't start on my way to get throttle body cleaner, unplugged CPS and re plugged it. Started fine, didn't cut out or dip in rpms much. Its got a lifetime warranty that ill take advantage of soon. Cleaned the IAC, mouth and butterfly of TB as best I could. Didn't see much of a difference but it felt better. Cruiser I know you reccomend a certain brand for the cps, what was it again?

cruiser54

Unplug the CPS again. Tweak the little barrel terminals so they grab the opposing pins tighter. Apply OxGard and plug it back together.