Now I have a bad idle

1989 XJ 4.0 4x4 auto 84,xxx miles

I have a new problem after doing the exhaust manifold gasket and everything else I did.

My jeep now idles bad. When I first start it it will idle fine for anywhere from 10 seconds to 30 seconds. Then it will idle down really low and will almost die. Then it will pick back up. It then will idle low and lope again. Repeat. Sometimes though it will sort of even out. If I cut the jeep off and start it right back then the low idle will come right back. And it has died twice.

Quick list of what I did and what's new.
1. New exhaust manifold gasket
2. 746 injectors
3. Cleaned TB & IAC (carb cleaner)
4. New down pipe
5. New flange gasket
6. New vacuum harness
7. Cruiser tip 31
All sensors worked before so I don't see how it's any sensors. One day it was fine and then I did the above and put back together and now it idles horribly. I was wondering if maybe I damaged the EgR on the side of the intake manifold. Maybe it's stuck now. I am going to try to check it. Can the egr be by passed?


I am currently still running nothing after the down pipe. Never have since day 2 and before I had part of my exhaust manifold gasket blew out. But I never ever had this problem until now. I am so disappointed that I tried fixing stuff and now it caused this.

Ok. I looked and read but I cannot understand what to do when testing EGR. What am I supposed to be pushing or pulling on, on the EGR? Also to test the with vacuum, do I unplug the vacuum line coming from the vacuum harness and put another vacuum line on there?

I can't find any pictures or videos of testing and I've went out and tried pushing and pulling but I'm not sure I'm doing it right. I'll keep searching until hopefully I get am answer.

PS: I was thinking could me having an exhaust manifold gasket leak all this time, until now, have essentially been a vacuum leak causing the EGR to not work or made it where I couldn't tell it was working or not? Or is that a stupid theory.

At low RPM's the EGR should be closed. The ECU opens it with the EGR vacuum solenoid. It usually opens around 1500 RPM.

The EGR is simple, a diaphram that opens (pulls) a piston allowing some exhaust gas into the intake manifold. There should be no bypass at low RPM's.

Plug off the vacuum tube going from the EGR solenoid to the EGR and it should stay closed.

On some models it is possible to see the diaphragm on the engine side of the EGR. A mirror and flashlight may be helpful. On some models the vent cutouts are too small to see in behind the diaphram. You may be able to feel it function with a finger tip when you apply and release vacuum. A couple of lite raps with the plastic handle end of a screwdriver sometimes helps it come unstuck. Not to hard, you don't want to dent it. Only two things generally go wrong with the EGR, it sticks or the diaphram tears. When the diaphram tears it often makes a noise when under vacuum, a sucking sound, a whistle or a croak.

Did you hook up your transducer/do you have a transducer?

Make sure you have power to the EGR vacuum solenoid with the key in the run position.

If you replaced injectors make sure the right connector is on the right injector, It is easy to swap the middle ones.

Hopefully you didn't mess up any connectors or wiring or screw up your IAC.

Carb cleaner isn't the best solution, it sometimes screws up sensors, the TPS is especially sensitive. Sometimes carb cleaner is so strong it eats the insulation off the insides of sensors or the IAC. The IAC is basically a tiny electric motor with tiny varnish covered windings inside, Carb cleaner can be basically paint remover. The TPS is sensitive to any liquids, solvents or water (especially water).

^ First thank you. I didn't think I'd get any answers.
My jeep seems to run fine down the road. It's only am idle issue or when I come to a stop sign. That wouldn't be the TPS, would it?

Second, I regret using carb cleaner. That way I could rule that out.

Third, I will try your suggestions on the EGR tomorrow (almost dark)

Fourth, I marked injectors wires before disassembly.

Fifth, I'm going to JY tomorrow to get 2-3 iac, 2-3 EGR's if I can find them. I can not afford new ones right now. No way.

I really don't get why it was fine the day before I took the stuff apart, then it's messed up after reassembly.

I'm going to try your ideas and swapping IAC and EGR first. Then I'm going to put back in old injectors just to rule that out as well.

I would believe it's not a timing issue or motor issue or it would have had it before.
Also Friday/Saturday I will be getting cat, muffler, & tailpipe back on. That way I'll have correct backpressure.

I'm leaning towards the IAC was damage from cleaner or I damaged o2 sensor or EGR when removing. I really pray The Lord helps me solve this, because I don't know what to do.

Went out and started it and idled descent for about 2 minutes. I unplugged the vacuum line at EGR solenoid (it's at firewall. I tried both) It changed nothing. Still idling ok @ about 2-3 minutes.

I then cut the jeep off and started it back and within 15 seconds the bad idle was back. I tried the EGR solenoid vacuum line again. Nothing. It kept loping and almost died but then it would pick back up.

It's now completely dark so I cut it off and came in.

All together the jeep ran about 3 and half minutes.

Edit: tomorrow I'm also going to check my spark plugs and see what they look like.

Try giving it a tiny bit of throttle at the TB, if the IAC is sticking and you can smooth the idle out at around 500-600 RPM's by hand, it is likely a IAC issue.

Swapping out parts hoping to get lucky may save some time and energy, but most times you'd be better off systematically troubleshooting.

And another tip, don't get fixated on components, sensors etc. Renix are known for flaky wiring and connectors. I think I've actually changed maybe 6 sensors in 26 years on mine, most times it is corrosion in a connector, grounds or some other issue. Getting oil or anything else in a sensor connector is likely to cause issues, most sensors are low voltage.

Not likely to be a TPS, they usually cause a really high idle when they get full of water or whatever. The exception is the TPS ground, which can cause a low idle or hunting idle. I've gotten water in mine doing a motor wash and screwed it up, other guys have said getting solvent in the TPS causes issues.

I would not swap out the EGR unless I was sure it is the issue. Taking that sucker out (if you can get it out) may cause some semi serious issues.

Lastly, make sure your battery is charged up, low voltage can screw with IAC function.

What you have going on may also be a vacuum leak, a very small vacuum leak can cause hunting at idle. Just the right amount of leak and the ECU has trouble trying to adjust.

One mistake first timers have when changing out a exhaust intake gasket is they don't get it seated properly when reinstalling. I doubt it, but yours may be sitting on one of the locator pins and you have a small gap between the intake and the head. Hard to see in there, look close, use a flashlight check the front and rear.

You can plug most of the intake vacuum ports for a test, except the fuel regulator, most of the vacuum lines going to the intake are for accessories or other stuff not necessary for the engine to run and see what happens to your idle. Look in the fuel regulator vacuum line for raw fuel, if it is leaking fuel into the intake it can cause issues.

Just a procedural tip, don't try to do too much in one bite. Especially when troubleshooting the sensors and harness. You disconnect too many connectors and find at the end of the day you have another issue and no idea where to look. If you do the work one bite at a time, you usually catch the screw ups earlier and don't have as much back tracking to do.

One bent pin or a pin that has backed out of a connector while you were putting it together, can screw up your whole day.

make sure you didnt bump the map sensor vacuum hose. it might be ever so slightly loose.

I've checked for vacuum leaks 3x with carb cleaner and can not find one.
I forgot to check spark plugs and it's dark again. But they were fine before and less than a year old.

I may try the cigarette smoke test to check for vacuum leaks again.

I am going to test TPS tomorrow and make sure it's getting correct voltage. It was less than a year ago when I checked it then.

I read you need a special tool to check IAC but I was wondering how do I check the grounds at connectors? Set my meter to ohms and probe the ground wire and then touch the other lead to it's ground.

So for IAC I would probe connector at ground wire and then touch other probe at dipstick ground. Is this correct? Also what ohms am I looking for to show the ground is good?

There really is no way to check the IAC for proper function. And checking the electrical is a waste of time, the IAC is basically a tiny reversible motor.

What you can do is look down the IAC orifice in the top of the TB and watch the piston move as you work the throttle with the engine running.

Ohm test the TPS ground wire, TPS side of the connector, to battery negative.

The easiest way is to run the TPS wires over the top of the rubber air intake tube and skin back a little insulation so you can get to the wire core.

90xj06 said:

make sure you didnt bump the map sensor vacuum hose. it might be ever so slightly loose.

Click to expand...

Good catch.

Make sure the MAP vacuum line is pushed into the right hole, there are two there on the engine side of the TB. One hole goes through to vacuum, the other is just a plug into a dead end.

The MAP vacuum line also tends to get tiny cracks in it.

8Mud said:

Good catch.

Make sure the MAP vacuum line is pushed into the right hole, there are two there on the engine side of the TB. One hole goes through to vacuum, the other is just a plug into a dead end.

The MAP vacuum line also tends to get tiny cracks in it.

Click to expand...

I know the map vacuum line is good. I just replaced it by doing Cruiser54's tip 31. I will double check the connection of the sensor itself. I've already checked once.

Chick-N-Picker said:

I know the map vacuum line is good. I just replaced it by doing Cruiser54's tip 31. I will double check the connection of the sensor itself. I've already checked once.

Click to expand...

A good mechanic is one who finds the problem and replaces what is necessary. Replacing something and saying to yourself all is good, is kind of like saying the operation was a success but the patient died.

What I'm getting from your post is the idle was fine before you started fixing things. Not knocking your efforts, most every mechanic has done it, built a problem into a vehicle while trying to fix something else.

Likely the best approach is to back track and double check whatever you have disconnected and reconnected.

If it isn't something easy and obvious it may be something subtle. The pins male and female in those connectors are held in with a tiny spring clip, sometimes when reconnecting the connector you dislodge the pin. Sometimes they backed out during original assembly at the factory, barley made contact for decades and you dislodged it when you moved the harness or disconnected the connector. I hold the connector and gently pull on the wires in back of the connector, anything that comes out easy has likely always been screwed up.

You may have melted the insides of your IAC with carb cleaner.
You may have melted the insides of the TPS with carb cleaner.
You may have split or wrongly connected a vacuum line. Those vacuum lines get stiff, moving them around can cause cracks.
You may have stuck the MAP vacuum line into the wrong hole on the TB.
You may have gotten oil into a connector, the TPS has like .8 volts going through it, it doesn't take much to mess with .8 volts.

TPS, vacuum leak, bad connection someplace or a faulty EGR are my best guesses. Could be a fuel issue, either volume, pressure and/or even electrical. The injectors you installed are a question mark in my mind. Personally I've never used any but cleaned and tested, used, OEM injectors.

Two common fallacies with young mechanics, new is better and I swapped it out so it is good. Old timers say if it ain't broke don't fix it and you are better off with a tried and proven component than some questionable Chinese junk fresh out of the box. New doesn't necessarily mean better, it just means new.

And last word of wisdom, it is what it is, not what somebody says it is.

On some models it is possible to connect the wrong connector at the fuel rail connector bundle.

I'm wondering how you managed to disconnect and reconnect all of the injector connectors without shattering one? The same with other 25+ year old plastic that has lived it's entire life in a 200 degree, fuel, oil, dirty environment. If you have a secret, please share it, I've never been able to do that? At the very least I usually snap off a few locking clips?

And lastly the real pain, where the injector harness makes the bend at the firewall is a trouble spot, every time the motor moves around it flexes that harness. You may have broken a wire inside the insulation where it is almost impossible to see. Not likely but it happens. I'm always real careful how I bend or flex that harness when removing the intake/exhaust.

I don't remember what the 746 injectors are rated at. Going with a larger injector without modifying the rest of the engine can lead to problems.

If nothing else, run a can of BG44K through the fuel. It will clean out the injectors and carbon.

This is rare, but for once I am going suggest we start from scratch and take a pass on some of 8mud's ideas for a minute.

First off, you do need to check the sensor grounds at the sensor to the battery negative post. they should be less than one ohm. If not you need to do Cruizer54s ground refresh steps and fix the poor sensor grounds. Two main spots are the sensor grounds at the engine block near the oil dip stick, and at the battery negative post.

the fact that your idle is hunting tells me the IAC is working.

A hunting idle, and not having any other issues is usually a vacuum leak (which you have covered), or a bad sensor ground or a problem with O2 SENSOR circuit!!!!!!

Also be sure to check the cap and rotor for excess wear and corrosion.

O2 sensor can be damaged wiring, a bad O2 heater relay that feeds 12 volts on the orange wire to the electric heater in the sensor. Or a bad ground, solid, less than 1 ohm grounds are critical for all sensors. Or the O2 sensor has a bad heater, or is contaminated and old, reading too slowly, responding too slowly to O2 reading changes.

Also the lack of a cat converter may be causing O2 sensor errors, lack of back pressure on the exhaust.

But one other major possibility is the injectors you installed. If they are more than 19 lbs of fuel per hour capacity, they are not able to restrict flow enough to maintain a steady idle IMHO. Many have tried higher flow injectors on a Renix jeep and failed, documented in older posts here. I have also had idle speed issues caused by a dirty or bad IAT, Intake Air Temperature sensor. Pull yours and clean it with a good brake cleaner fluid. Test it at room temp and in boiling water to see if the ohms reading of the loose cleaned sensor is close to the factory FSM spec (posted in old threads here).

Also one of the new injectors may be bad. Test this, and test the spark, etc for each cylinder, by disconnecting the injector power one cylinder at a time (or one secondary spark plug wire at a time, your choice) to see if one cylinder is not working right. It should make the engine run rougher, if not you have a bad cylinder to check out, bad plug wire, spark plug, injector, or injector wire, etc.

old_man said:

I don't remember what the 746 injectors are rated at. Going with a larger injector without modifying the rest of the engine can lead to problems.

If nothing else, run a can of BG44K through the fuel. It will clean out the injectors and carbon.

Click to expand...

The Bosh (volvo) 746 is 20.2 lbs per hour according to one data sheet. About 1.5 lb more than OEM spec. Seems several folks have used then on Renix with good reports, including cruizer54. I did read there is more than one type of 746 injector?

http://www.jeep4.0performance.4mg.com/tech_specs.html

That link is a huge great resource for data on heads, mods, and injectors, right up your alley old_man .... IIRC you have a stroker?

According to the data I found it was the same flow as stock. However there is 2 different 746 injectors. But I don't think the other one has the same wire connector.

Also sounds about the time the system goes into closed loop. Might be an o2 issue or damaged harness.