YJ stumbling

[Atlas]

Hi guys

I'm back. Forgot I was a member here and I was deleted. I have spent alot of time learning about car mechanics and everything has been good so far.

Need some help this time

94 2.5L 150k 5 speed

At cold start up engine revs to about 1800 rpms then goes down to about 750 ish

I go in gear and get moving and suddenly it hesitates a few times then clears up. Second is worse sometimes if I don't get the hesitation in first. So I drive it and it runs good. I can hit 4k+ rpms in second. I can push the clutch in and floor it to the reddline. Safely of course, I just wanted to see if it could


So then I'm at 180 degrees or less and I turn it off. Turn on high idle for a few seconds and more spit and sputtering.

Huh. Drives me crazy.

Here's what I've done so far

Plugs
Wires
Cap
Fuel filter
Air filter
Tps
Map sensor
Cleaned the tb and new gasket
Tightened valve Cover bolts

Changed the stat to a 180 because the old one was sticking. It was doing the same problem with the 195 stat
Techron chevron injector cleaner
Brand new flow master two days ago to replace rotted muffler

I sprayed all around the intake and all the vacuum lines for leaks and no change in motor sound.

I'm at a point where it's going to take some know how to figure this out
List of possibles
Idle air control is bad completely
O2 sensor?
fuel pump?
Catalytic conveyor?

Possible timing?

Problem is I don't know enough to say which part would make this so intermittent. I can read ideas all say but I need to broaden this more


This just starting happening in November. I drive it daily.

Can we do some brainstorming?

 

[Saddle Tramp]

I’d look for a vacuum leak if you don’t have any codes.

 

[Atlas]

Yeah doing some more research I read that on some of the fittings going into the intake there might be hidden leaks. I plan on giving it hell with some tb cleaner tomorrow.

Yeah no codes ever come up.

Oh one thing. At running temp the idled drops to 500

 

[luis]

how come you went down to 180? Iv always been told that you have to keep the the thermostat at 195. It's what the engine wants to run at to be efficient. I had a similar problem on my tj the thermo was opening to soon and not letting it get hot wasn't running as good. After I replaced it I notice it was running and idling better. Not saying it could be causing your issue but it could be a start. Have you checked your fuel pressure? If not try hooking a gauge to the rail and see what your getting at idle, then give it alittle gas and see if it drops. Hope that helps

 

[Atlas]

I'm running a 180 because it keeps me cooler in the summer. My friends Yj has the same stat

My problem happens when it's cold

Yeah I'm going to test the pressure out as well. I need to buy a gauge.

The issue is intermittent at start up. Boggles my mind. I know once the computer realizes what's going on it searched back for a setting that will accommodate the issue. I just need to figure the issue out. Could be its telling the map sensor to regulate the fuel due to a week pump or Tps letting less air in due to a vacuum leak or O2 is messed up. Or? Lol.

 

[luis]

I'm running a 180 because it keeps me cooler in the summer. My friends Yj has the same stat

My problem happens when it's cold

Yeah I'm going to test the pressure out as well. I need to buy a gauge.

The issue is intermittent at start up. Boggles my mind. I know once the computer realizes what's going on it searched back for a setting that will accommodate the issue. I just need to figure the issue out. Could be its telling the map sensor to regulate the fuel due to a week pump or Tps letting less air in due to a vacuum leak or O2 is messed up. Or? Lol.

In that last part any of those problems should trip the cel. But then again the obd 1 computers were always alittle hard to work with. You don't need to buy a gauge. Autozone or any other parts store should rent them out for free ( you pay full price for the tool and when you return it you get your money back)

 

[heepjeep]

I got the same problum with mine kinda like miss fiers till I get warm I'm diggin around on mine for vac. Leaks but I'm just got it so there a lot of stuff that ganna be renewed even if I don't need it wanna make it fresh but ill let u know if I fined it

 

[Atlas]

Update

Went to advanced and they don't rent the gauge. Autozone was closed for some reason

Here's what I did.
Sprayed all the vacuum lines. Nothing happened with the engine
Sprayed the intake the best I could. Nothing

Got underneath and wiggled the O2 sensor wires. No change but I got a code
21 O2 not reading lean of rich. Essentially bad O2 I guess

Took it for a short drive and it drove fine. When it's warned up it doesn't stumble

Got back and reset the computer. While it was doing that I got underneath to inspect the O2 wiring. Found that the retaining clip has broken off and it was possibly unplugged. I inspected the old wires and nothing was fraid or oily. Reconnected the plugs and set it back in the retainer.

Safe bet PO had replaced the O2. This Yj has alot of new parts. Makes sense why the clip was broke

Started it up and drive around and no code.

I'll let it cool off so I can see if my problem comes back.

 

[Atlas]

No change when cold. Hmm

 

[808CJ7]

I'd try a new 195 stat. You stated the old one was sticking when you swaped to the 180. Might be confusing the the computer. Might be reading that it's not at operating temperature. Is you friends yj fuel injected or carb. Carbs aren't as picky

 

[Atlas]

He has a 93 2.5L

I'm ruling out the stat only because this problem started in November. In January we added more coolant to lower the freezing point to -45. When we did that I started running a little hot and the stat didn't open until 225 degrees. Once we changed the stat everything stayed cool but not so much heat


I just tested my cts. My first time with a multimeter. I think my reading is 1050. Engine is cold and it's 34 degrees out

This is very confusing as it only does this on start up.

Idle air control not returning back to position?

 

[luis]

He has a 93 2.5L

I'm ruling out the stat only because this problem started in November. In January we added more coolant to lower the freezing point to -45. When we did that I started running a little hot and the stat didn't open until 225 degrees. Once we changed the stat everything stayed cool but not so much heat

I just tested my cts. My first time with a multimeter. I think my reading is 1050. Engine is cold and it's 34 degrees out

This is very confusing as it only does this on start up.

Idle air control not returning back to position?

Disconnect the idle air control valve and see if anything changes with the idle. I know here in az around November is when it starts getting cold so I difference in thermostat would make a difference. But thermostats are dirt cheap. So I'm confused you said it started to run better with the o2 sensor plugged back in? Is it running better after you cooled it down? Sorry I'm just confused and want to help you solve this issue

 

[Atlas]

Initially when I restarted after inspecting the O2 it ran fine. But I think that is because it was at operating temp

After it cooled down it was stumbling. It warmed up and was ok.

A cold start with a different stat won't do much with the idle as the sensors are not working yet and it's in default. The stat is closed so the cts isn't reading yet to communicate coolant temp

 

[superj]

is the temp sensor good? the one for the ecu, not the one for the gauge?

 

[luis]

When is autozone opening back up? We need to rule out fuel pressure as the cause of the poor idle

 

[Atlas]

I tested the cts at the thermostat housing when it was cold. Gave me 1050 as a reading. I didn't know the part about starting it up for two minutes then re testing

I hope tomorrow for autozone. I can do the entire test in the parking lot in like 5 minutes. Damn gremlins.

I also tested my old tPs. A and B read .08 B and C read 4.88. So I basically had a good Tps all along but I still replaced it.

 

[luis]

I tested the cts at the thermostat housing when it was cold. Gave me 1050 as a reading. I didn't know the part about starting it up for two minutes then re testing

I hope tomorrow for autozone. I can do the entire test in the parking lot in like 5 minutes. Damn gremlins.

I also tested my old tPs. A and B read .08 B and C read 4.88. So I basically had a good Tps all along but I still replaced it.

1050 ohms? What does your temp gauge read? I don't think its a temp issue but could be wrong. It may be fuel or pcm related since it runs fine after you warmed it up. Did the code pop back up?

 

[Atlas]

The temp is on the larger line between 100 and 210. Sometimes it goes up and comes back down. That's the stat working. Also it's cold out so that has been cooling things off faster.

No codes at all have come up since I inspected the O2

PCM? Hmm

I have to check the fuel pressure!

 

[JPNinPA]

When you cleaned the TB did you take it off and remove the IAC and clean this as well? If not you should. This will give idle issues. hot or cold.
TPS will have flat spots when they go bad, so when you gradually step on the gas you will not increase RPM for a bit then it will jump and catch up. TPA should be OE brand or else early failure.
What plugs do you have? Autolite AP985?
What brand O2's Bosch brand seem to five issues. Slow up stream O2's will cause rough idle until at temp. Check the part # to be sure you have the correct ones in and in the correct locations.
Cold the temp sender should be high res. At 210 it should be low like 9 ohm or 90 ohms. I'd have to look it up.
You really need a 195* thermo. At cooler temps your waisting gas and slowly killing your CAT. Not to mention poor heat. The fact you added coolant and started to overheat is either the wrong % mix or another issue you need to fix.

 

[Atlas]

Yes we cleaned the iac with tb cleaner which was removed from the tb
I can put the oem Tps back in but even with that I have the same issue
Same problem before the plugs and wires
Problem presents itself when cold and computer is ignoring the O2 except when I havd brought it to temp and restarted after 5 or so minutes but the engines cools down fast

I believe the stat was faulty and that's why I has large sweeps in my gauge. Yes the mix is more coolant rich but maybe 60/40. That is allowable due to cold temps

I don't have any large sweeps now. Everything ran fine until it got cold out

Could a weakening battery cause all this?