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Fluctuating idle and stalling

T

tylergrant2011

NAXJA Forum User
Location
Luverne
I know this topic has been covered in many threads but I can't pin point to the right culprit. I have a 88 xj 4.0 that the idle fluctuating on. It will idle normal then drop then go back up. Sometimes when I go to a stop (1/3 times) it will die and I have to start it back up. Also the check engine light isn't on but the indicator don't even show when u turn the key. Any suggestions?
 
Fix the light first, then you can get the codes its throwing. I'd be checking vacuum lines, dirty throttle body, pretty much all sensors, alternator, battery and battery cables, fuel pump, fuel pressure regulator and fuel injectors.
 
dan1977p said:
Fix the light first, then you can get the codes its throwing. I'd be checking vacuum lines, dirty throttle body, pretty much all sensors, alternator, battery and battery cables, fuel pump, fuel pressure regulator and fuel injectors.
Click to expand...

if i am not mistaken the renix era (87-90) or even before doesnts store the codes on the pcm. in 1991 when they introduced the obd1 was when you could test the codes correct?
 
tylergrant2011 said:
I know this topic has been covered in many threads but I can't pin point to the right culprit. I have a 88 xj 4.0 that the idle fluctuating on. It will idle normal then drop then go back up. Sometimes when I go to a stop (1/3 times) it will die and I have to start it back up. Also the check engine light isn't on but the indicator don't even show when u turn the key. Any suggestions?
Click to expand...

There is no check engine light on an 88, and no codes. My best bet would be one or more small vacuum leaks or loose ground crimps in the wiring harness for the sensors, or loose dirty ground connections on the sensor wire ground connections near the oil dip stick on the block. That assumes the distributor cap, rotor, spark plugs and wires are in decent shape and the ICM/HV coil is OK.

Work long and hard on the tiny vacuum leaks, valve cover gasket, throttle body gasket, loose bolts on the intake-exhaust manifold, and the entire CV vent system, Map to throttle body vent hose and other vacuum hose tubing and hoses, common issue on an 88 and do the same with an ohm meter on all the sensor grounds, using ohms with the engine off. They must be under 1 ohm from the sensor to the battery negative post.

Later check the power to the O2 sensor heater, and the O2 sensor heater itself.
 
Ecomike said:
There is no check engine light on an 88, and no codes. My best bet would be one or more small vacuum leaks or loose ground crimps in the wiring harness for the sensors, or loose dirty ground connections on the sensor wire ground connections near the oil dip stick on the block. That assumes the distributor cap, rotor, spark plugs and wires are in decent shape and the ICM/HV coil is OK.

Work long and hard on the tiny vacuum leaks, valve cover gasket, throttle body gasket, loose bolts on the intake-exhaust manifold, and the entire CV vent system, Map to throttle body vent hose and other vacuum hose tubing and hoses, common issue on an 88 and do the same with an ohm meter on all the sensor grounds, using ohms with the engine off. They must be under 1 ohm from the sensor to the battery negative post.

Later check the power to the O2 sensor heater, and the O2 sensor heater itself.
Click to expand...

I appreciate that information so your saying the ground on all sensors must be less than 1 ohm? I've checked for vacuum leaks in fact wasted a whole can of ether spraying around the vacuums either hoping to find a leak or a big kaboom. I'll check the plugs wires cap and button.
 
Installed the Bosch upgrade injectors in my jeep. It takes like 4 seconds to start now. It seems to be running rich and burning tons of gas. Is this normal for injectors or do I have defective ones.
 
The ground resistance from the negative battery to firewall was .4 and the resistance ground for map ground was 6.5 that might be my problem. Gonna check those sensor grounds that are crimped and duct taped. Anywhere else to look?
 
tylergrant2011 said:
The ground resistance from the negative battery to firewall was .4 and the resistance ground for map ground was 6.5 that might be my problem. Gonna check those sensor grounds that are crimped and duct taped. Anywhere else to look?
Click to expand...

Tyler, go to www.cruiser54.com and complete Tips 1 through 5 before going down any other rabbit trails.
 
cruiser54 said:
Tyler, go to www.cruiser54.com and complete Tips 1 through 5 before going down any other rabbit trails.
Click to expand...

I've did the first 5 tips with slight improvement I also soldered the grounds for the sensors the brown and white ones with the duct tape to a 10 gauge wire and grounded it to the engine. I've noticed when the problem occurs the worse. When I was sitting in the yard after the engine was warm. I could punch the gas and then let off and the idle would drop and sometimes stall.
 
tylergrant2011 said:
I've did the first 5 tips with slight improvement I also soldered the grounds for the sensors the brown and white ones with the duct tape to a 10 gauge wire and grounded it to the engine. I've noticed when the problem occurs the worse. When I was sitting in the yard after the engine was warm. I could punch the gas and then let off and the idle would drop and sometimes stall.
Click to expand...

Okay, good.

Oxygen sensor is suspect as are vacuum leaks.

Are your intake manifold bolts good and snug?

When's the last time you treated it to plugs, wires cap and rotor along with a throttle body and IAC cleaning?
 
cruiser54 said:
Okay, good.

Oxygen sensor is suspect as are vacuum leaks.

Are your intake manifold bolts good and snug?

When's the last time you treated it to plugs, wires cap and rotor along with a throttle body and IAC cleaning?
Click to expand...

I've sprayed a half a can of carb/tb cleaner around the intake, vacuum harness, tb, brake booster, pretty much everywhere with no change in idle. I used the rest to clean the IAC and tb. Still no luck. I've upgraded the fuel pump ground by cleaning the terminal and mount behind brake light and added more 10g wire from ground wire on harness of fuel pump to the body. Still no change. Spark plugs are brand new. But wires are a few years old. And cap and button are original but still appear to be in good shape. I shined the points up in the cap and rotor.
 
Another thing I might add is it seems to run better if I disconnect a vacuum line or two. It also seems to be running rich. You can smell a little raw fuel coming out of exhaust.
 
cruiser54 said:
You might have a bad MAP sensor or poor/low vacuum source to it.

BTW, plugs, wires, cap and rotor are due to be changed every 30,000 miles....
Click to expand...


I'll give it a new tune up. Also I'm not sure if this may help any but whenever I unplug the IAC while it's running there is no change.
 
I found the problem. I was pulling of the plug wires one by one while it was running to hear change in idle and to find possible misfire. I got to #4 grabbed the boot and it knocked my boots off. Now the last question is what plugs and wires to use or does it matter. Personally I'm a fan of ngk plugs
 
It may be a mechanical issue.Check your IAC, the Renix ones can fail or the plunger stick in the throttle body. Pull it and make sure it and the throttle body are clean. I've had the same problem and the plunger on the IAC was sticking in the bore. Changed it out, cleaned the throttle body and problem gone.
 
tylergrant2011 said:
I found the problem. I was pulling of the plug wires one by one while it was running to hear change in idle and to find possible misfire. I got to #4 grabbed the boot and it knocked my boots off. Now the last question is what plugs and wires to use or does it matter. Personally I'm a fan of ngk plugs
Click to expand...

NGK all the way.

As for wires, I prefer Taylor 84248 available from Amazon.
 
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