Bogged down with low RPM'S

Ive been on here long enough to search first and I have but my problem can be one of many issues and due to relentless rain and the need to drive this daily I'm hoping I can be pointed in the right direction of where to start first. '89 4.0 auto with the power/comfort feature and I'm sorry I cant remember if that makes any difference. Here's my issue. Really low idle, at the first mark on RPM's so that's 250? Strong fuel smell and when accelerating in doesn't speed up just feels bogged down and jerks a little bit and the RPM guage bounces around. Had a few cracked vacuum lines that I just replaced and just did cap/rotor. A persistant problem it has is every once in awhile it wont start and just turns over so I get out and wiggle the wire at the back of the engine that is a ground for something that people say is a Renix killer but after wiggling it starts right up and doesnt happen all the time so not sure if it has to do with my new problem. When in park or nuetral I can rev up the engine with little hesitation but when driving it bogs down so could it be transmission though I've had no problems before? I'm sure its a stupid sensor but where do I start and where can I find a sort of map of these sensor locations? O2 sensor has 5,000 miles on it max if that helps. Sorry for the long post I just need to figure out the problem while giving as much info as I can. Thanks.

Ok, sounds like you could have a number of different issues going on.

First, and foremost, clean secure grounds are ESSENTIAL for Renix era XJs to function. Poor grounds will cause more issues than you could ever imagine. There is only ONE unibody ground--a POS braided strap from the head to the firewall--if that is the "wire" you wiggle, well, it would explain a lot. Replace the braided strap with a 4 or 2 gauge cable. STRIP the metal on the head and firewall down to shiny bare metal. Treat the metal with an anti-corrosion agent from any paint/hardware store. Make the connections TIGHT. Ok, now lets move to the OTHER critical Renix grounds. Attached to the dipstick is the ground for the ECU--critical--the ground for the ICM/coil--critical--the ground for the o2 sensor--critical--and some others. Same as the cable for the unibody ground--strip to bare shiny metal, treat with anti-corrosion agent, make the connection TIGHT.

Now, the IAC mounted in the throttle body is the "muscle" for the ECU when it comes to idle speed. The IAC is a stepper motor that responds to ECU commands to extend/retract and change the idle speed. This can all be screwed up by poor grounds--starting to see a theme here? Ok, as a high idle can be caused by an intake leak--leaner mixture, higher the idle--too rich of a mixture can cause a low idle. Your XJ should idle at 700-750 RPMs after 20 minutes of driving (fully warmed up), with the transmission in DRIVE with the parking brake applied and someone's foot on the service brake pedal. Ok, things that make the engine run rich--poor grounds screwing with the sensors/ECU (theme continues), an exhaust leak upstream of the o2 sensor or a poor o2 sensor ground (theme), vacuum line fell of the MAP sensor on the firewall or out of the throttle body, a bad CTS (coolant temp sensor in the driver's side of the block under the manifolds), bad FPR (fuel pressure regulator), bad thermostat (engine running too cold).

Here is everything you need to know about Renix sensors and how to test them with a multimeter: http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

Here is an excellent article on upgrading the charging system: http://www.olypen.com/craigh/charge.htm

And, not to forget the EGR system including the vacuum transducer valve:

TEST your EGR system, info from 90 FSM:

Warm the engine to normal operating temperature.

Operate engine at idle speed.

Check vacuum at solenoid vacuum source.

Disconnect the hose and attach a vacuum gauge to it.

Vacuum should be at 17 inches.

If vacuum is low, check the line for kinks, twists, or a loose connection at vacuum connector on intake manifold.

If vacuum is ok, remove gauge , reconnect the line and proceed to next step.

Check vacuum at solenoid output port.

Disconnect the line and attach a vacuum gauge to output port. Vacuum reading should be 0 at this side of solenoid.

If vacuum reading is 0, leave the gauge connected and proceed to the next step. However, if vacuum is present check solenoid/ECU operation with the DRB-ii tester.

Disconnect electrical connector at solenoid and note vacuum at output port. Vacuum should now be present at output port.

If vacuum is present, proceed to EGR valve test. However, if vacuum is not present, replace the solenoid. Test the EGR valve as follows:

Leave solenoid electrical connector disconnected. Note engine idle.

The engine should idle roughly or stall. If this occurs the valve is ok. If the idle does not change, proceed to next step.

Disconnect hose from the EGR valve and connect a hand vacuum pump to EGR nipple.

Apply a minimum of 12" of vacuum to the valve and note engine idle. If engine now idles rough inspect the vacuum line between the EGR valve and the solenoid.

If the idle did not change, remove the EGR valve and inspect the valve and the exhaust passage in the manifold for blockage, repair as necessary. If no blockage is present replace the EGR valve.

TRANSDUCER VALVE:

Disconnect the transducer vacuum lines and the back-pressure line (bottom). Remove the transducer. Plug the transducer output port. Apply 1-2 pounds air pressure to the back-pressure port. Apply a minimum of 12 inches of vacuum to the input port. Replace the transducer if it will not hold vacuum.

Well, that should keep you busy for 5-10 minutes checking and testing all of that.

Also, are you still running the stock OEM injectors--the Jeep fire-starters? Read this JP Magazine article: http://www.jpmagazine.com/techarticles/engine/154_0811_preventing_jeep_engine_fires/index.html

Also again, don't forget to check and adjust the TPS to specs.

Also again and again, adjust the throttle pressure cable: http://www.naxja.org/forum/showthread.php?t=1015963

Keep the power/comfort switch in the power position.

Thanks for the reply. Sounds like good times ahead for me LOL I know people may have something to say about this but I took out my thermostat this summer because Redding heat had me running very hot and so I know it would run richer but haven't had any problems but for the last day so maybe the cold has it running way too rich though it's been cold for awhile and it just started acting up but I will get it back in today for starters and I know that ground strap is shot so it's time to do that too. It was a toy that barely got used up until a week and a half ago and now its my daily driver again so I need to start working on it and taking care of things. Thanks for the good advice.

No problema.

Describe your overheating issues.

Overheating was solved by replacing hoses that were filled with junk so water flow was minimal and then I just left the thermostat out because it wasnt being driven regularly. In inspecting vacuum lines and such I had found that the mechanical device attached to the firewall on the passenger side that has a cable going to the throttle cable, that the cable itself is limp and when applying throttle it does not tighten up or move at all. I'm sorry I'm not hip to what that device is or what it does so what it is? It's not EGR because it isnt the right place for it and doesnt look at all like it. Could the fact that the linkage too it does not tense up or move have anything to do with my problem?

Also my issue is it's runs good for the first minute and then starts acting up. I'm currently going piece by piece and checking over stuff.

Here's a pic of what I'm talking about along with the loose cable that goes to the throttle. I disconnected the electrical to this beast and nothing happened as for throttle response and such.

Cornflake said:

Overheating was solved by replacing hoses that were filled with junk so water flow was minimal and then I just left the thermostat out because it wasnt being driven regularly. In inspecting vacuum lines and such I had found that the mechanical device attached to the firewall on the passenger side that has a cable going to the throttle cable, that the cable itself is limp and when applying throttle it does not tighten up or move at all. I'm sorry I'm not hip to what that device is or what it does so what it is? It's not EGR because it isnt the right place for it and doesnt look at all like it. Could the fact that the linkage too it does not tense up or move have anything to do with my problem?

Click to expand...

That sounds like your cruise control servo, don't worry about it--unless you want to use the cruise.

Cornflake said:

Also my issue is it's runs good for the first minute and then starts acting up. I'm currently going piece by piece and checking over stuff.

Click to expand...

Good, you will learn more about your rig. Follow that link to lunghd.com and bookmark it, good stuff there. You can also pull your sensors and clean them, especially those in the coolant as scale can build up. Remember that single wire sensors ground through the sensor body so you need to use a electrically conductive thread sealer or none at all on them.

Cornflake said:

Also my issue is it's runs good for the first minute and then starts acting up. I'm currently going piece by piece and checking over stuff.

Click to expand...

Yeah, once you get done working through the stuff I suggested earlier post up if things are better/worse/same.

Good luck.

PS--the EGR system is on the driver's side of the engine. There is an EGR solenoid mounted on the fenderwell, the EGR valve is mounted to the intake manifold with a tube down to a bung on the exhaust manifold, and the vacuum transducer valve is a round plastic disc with two nipples 180 degrees from each other and a third nipple on the bottom--that nipple likes to burn off against the exhaust manifold.

Thanks for the help. I figured it was cruise control so I will leave it alone since I dont ever use it. Done for the night as it is getting cold and dark but I will keep posted as to what I find. Thanks again for the help