Low / rough idle once engine is hot 1994 FZJ80

[hbange97]

Hi all,

1994 FZJ80 starts up great and runs well for about 30 minutes when I come to a stop. Idling is pretty row and drops below 500rpm. Get a pretty strong fuel smell from the exhaust as well.

Think O2 sensor based of what I've read. Anyone have a similar problem or any suggestions how to diagnose/fix?

Video: https://1drv.ms/v/s!AlZxhe8MR5o0gv9-Tf5o4vXhcuTLJw

Cheers

 

[voodu3]

O2 sensors are a good place to start. Did you ever get a check engine light? Have you tried to pull codes off the ecu? Do you still have Cats? I’ve had a similar issue and I’ve narrowed it to clogged catalytic converter. I’m in the process of replacing the exhaust so I don’t know for sure but running with just exhaust manifolds it hasn’t stumbled.

 

[devo]

The IACV and TPS can cause those symptoms also and they do not throw codes! Definitely make sure your exhaust is not clogged .

 

[ajax1]

I’ll vote ecu coolant temp sensor

 

[hbange97]

O2 sensors are a good place to start. Did you ever get a check engine light? Have you tried to pull codes off the ecu? Do you still have Cats? I’ve had a similar issue and I’ve narrowed it to clogged catalytic converter. I’m in the process of replacing the exhaust so I don’t know for sure but running with just exhaust manifolds it hasn’t stumbled.

Thanks mate. No engine codes and problem only comes on intermittently. Will look to check exhaust next.

 

[BILT4ME]

Could also be the harness by the EGR and having partially melted wiring that is intermittently shorting out and grounding the injectors, causing them to stay open, hence the heavy fuel smell. This would also mess with O2's and may throw a no fire code on any given cylinder. I know you have no codes yet, but maybe it hasn't happened in the right frequency to be a problem.

I Also think the IAC and the VSV could need attention.
Check all your vacuum hoses to make sure something didn't come off.

 

[hbange97]

Could also be the harness by the EGR and having partially melted wiring that is intermittently shorting out and grounding the injectors, causing them to stay open, hence the heavy fuel smell. This would also mess with O2's and may throw a no fire code on any given cylinder. I know you have no codes yet, but maybe it hasn't happened in the right frequency to be a problem.

I Also think the IAC and the VSV could need attention.
Check all your vacuum hoses to make sure something didn't come off.

Thanks that is very helpful.

First point of call is the O2 sensor i think. I have seen people suggesting to disconnect them and see if the problem goes away.

Is there any risk of damage from driving with them disconnected for a few days?

 

[BILT4ME]

Thanks that is very helpful.

First point of call is the O2 sensor i think. I have seen people suggesting to disconnect them and see if the problem goes away.

Is there any risk of damage from driving with them disconnected for a few days?

Jut replied to you in the other thread....

Is your truck OBD2?

If so, get a reader like UltraGauge and watch the readings on the O2 while driving.

Running with O2 disconnected, it will drink the fuel. You may end up with more codes. but, will it "hurt" it? No.

You can also pull the main fuse (ECM?) in the fuse block for about 60 seconds and it will clear existing settings and may help clear up issues. It's like disconnecting the battery.

 

[hbange97]

Jut replied to you in the other thread....

Is your truck OBD2?

If so, get a reader like UltraGauge and watch the readings on the O2 while driving.

Running with O2 disconnected, it will drink the fuel. You may end up with more codes. but, will it "hurt" it? No.

You can also pull the main fuse (ECM?) in the fuse block for about 60 seconds and it will clear existing settings and may help clear up issues. It's like disconnecting the battery.

Not sure if its OBD1 or 2. How do i check?

Apologies I am newbie here and have quite a bit to learn!

 

[BILT4ME]

Not sure if its OBD1 or 2. How do i check?

Apologies I am newbie here and have quite a bit to learn!

What year is it?

If it is 1995+ it should be OBD2.

However, I'm not sure if that is all countries.

@mudgudgeon may be able to advise on this.

Based on your other video, I would lean toward the IAC valve and the VSV.

 

[hbange97]

Its a 1994 in Australia.

Thanks for your help. If the O2 sensor dont improve anything they're next on the list to check off.

 

[devo]

Have you tried a simple ECU reset? Pull the ECU relay wait 15 minutes, reinstall then start the engine. Sometimes this helps with clearing any electronic gremlins.

 

[hbange97]

Have you tried a simple ECU reset? Pull the ECU relay wait 15 minutes, reinstall then start the engine. Sometimes this helps with clearing any electronic gremlins.

Is that the same as the Circuit Opening Relay below?

 

[CrabCake]

Is that the same as the Circuit Opening Relay below?
View attachment 3711068

No, if you are a '94, you should be OBD1 and it's in the fuse box right behind the charcoal canister. It should be marked EFI on the top of the cover and be a 15a blade style fuse (just like the ones under your dash). Pull the fuse straight out and let it sit for 15 minutes as others have said.

One note, once you re-set the ECU, it will need to re-learn the idle characteristics. Idle will be crap upon first startup and you'll be nervous...just take it out for a drive like normal, maybe stop in a parking lot and shut down & restart to give it another cycle, should be smoothed out pretty quickly after that.

On the OBD1 trucks, the CEL is pretty slow to come on...usually needs to run like crap constantly for a while before the CEL triggers. You can use a jumper wire in the plug harness on the firewall passenger side, take a look at other threads for an easy way to count the CEL flashes on the dash after you put the jumper pin in the right places and turn the key to run position. If you have codes, report back.

One personal experience on O2's...when I bought mine and drove cross country, it did just what you are describing about 3/4 the way home (2k miles so far, 1k to go). Eventually triggered the CEL. What I found was water that had gotten into one of the O2 connectors during a very heavy storm while driving on the highway....water ran out of it weeks after I got home and disconnected one of the O2's. Blew it out with compressed air, put some dielectric grease in it, taped up, and never had a problem since for 2 years now, including heavy wheeling in pretty deep mud/water holes.

I can take pics in a day or so if you need visuals on the fuse box and a proper way to do the CEL check, but lots of photos here if you look a bit.

Good luck!

Update, here's a pic (borrowed from Ebay) of the top of the fuse box, pull the one marked EFI

 

[mudgudgeon]

AFAIK the earlier Aussie 80's aren't OBD1, I think, but not certain, they used TOYOBD or some other protocol (Toyota used a few).

Pre 95, scangauge won't work.
You need an alternative like Engine Watchdog, or try to get hold of a ZF Scanner / TOYOCOM reader. Works with pre 93,94 80s.

Thread 'Toyocom OBD1 Bluetooth available again' Toyocom OBD1 Bluetooth available again - https://forum.ih8mud.com/threads/toyocom-obd1-bluetooth-available-again.1136285/

I think 95 on 80s went to OBD2 in Australia, but not certain.
I believe USA mandated OBD2, and that it be readable by consumers, 3rd party mechanics etc
I don't think that was a requirement in Aus.

 

[mudgudgeon]

My Aussie 93 engine bay fuse box looks the same as what @CrabCake posted.

 

[Joelopy]

My 93 has the older ECU. It has personality and occasionally needs that 15 minute nap / attitude adjustment
Check your air tube- hard or soft? I cracked hard tube changing my first air filter. Weeks later it caused a similar stumble at the first complete stop after warm up.

 

[hbange97]

Thanks all. Disconnected the ECU fuse and that seemed to help. Has done rough idled once but that could have easily been in the re-calibration stage.

Regardless got the new O2 sensors and went to instal. Upstream one looks as old as the car and wont be easily to replace:

Downstream of the cat converter looks like a new muffler and pipe work without any sensor. Couldnt see it or the plug anywhere? Could this be part of the problem if the exhaust/muffler has been replaced without the downstream sensor?

New pipe connection down from cat converter;

 

[AussieHJCruza]

What year is it?

If it is 1995+ it should be OBD2.

However, I'm not sure if that is all countries.

@mudgudgeon may be able to advise on this.

Based on your other video, I would lean toward the IAC valve and the VSV.

We never got an OBD2 FZJ80, everything here is OBD1. Jan 1st 2006 was the cutover to OBD2.

Haven't worked on a pre-95 80 for a little while, but do I recall correctly that the AU market 1FZ vehicles from 08/1992 to 01/1995 have oxygen sensors?

 

[AussieHJCruza]

Thanks all. Disconnected the ECU fuse and that seemed to help. Has done rough idled once but that could have easily been in the re-calibration stage.

Regardless got the new O2 sensors and went to instal. Upstream one looks as old as the car and wont be easily to replace:
View attachment 3711929

Downstream of the cat converter looks like a new muffler and pipe work without any sensor. Couldnt see it or the plug anywhere? Could this be part of the problem if the exhaust/muffler has been replaced without the downstream sensor?

New pipe connection down from cat converter;

View attachment 3711931

AU market trucks don't have a cat, unless one has been added? The front 'box' is a muffler/resonator. If it has any, you should only have one O2 sensor.

Remember the majority of the vehicles on here are USA market vehicles which have EGR, Cat Converters, Oxygen sensors etc.