Low Rough Idle After Changing Battery (1 Viewer)

[DesertCruiser80]

Hello,

I recently got a '92 FJ80 and have been working out the kinks to get to run better. The truck was bought with a broken ignition cable for the 6th cylinder. I have replaced spark plugs, cables, distributor cap and rotor. The engine was still idling rough and at low RPM after that so I was recommended that I gap the plugs. (I thought they came gapped.) I gapped the plugs today and most of the rough, low idle was gone. Truck was idling quite well and felt more powerful.

I then went to get the battery tested and it was shot. I went to Walmart and got one. After installation, the engine takes just as long to start up as with the old battery and the rough, low idle is back.

Does anyone have any suggestions? I don't understand how changing the battery could mess with the low idling.

Thank you!

 

[Chris Wilcox]

One thing I have heard of but not experienced is that the fusible links can cause rough idle. Since they are part of the starting circuit maybe that is something to investigate. A new one isn't too much money.

 

[DesertCruiser80]

Where are the fusible links? Can't seem too find the location online.

 

[BILT4ME]

Fusible links are directly on the battery cable that you would have just changed. They are on the same bolt as the cable going to the starter.

Also, the engine will run rough for a number of starts after a batery replacement because it clears any computer settings.

Look through the attached thread.

The battery on your 92 is on the right side, not the left as the later models.

Fusible link question

Has anyone got a Toyota part number for this and the junction box?

forum.ih8mud.com

 

[ppc]

Disconnecting the battery resets the ECM and takes several starts and short trips to relearn. Don't panic until then.

 

[DesertCruiser80]

My battery is on the passenger side of the truck.

Do you know about how long the ECM takes to relearn?

Thanks.

 

[BILT4ME]

My battery is on the passenger side of the truck.

Do you know about how long the ECM takes to relearn?

Thanks.

It's something like 30 stop/start sequences. Not about how long, but most start it and drive it on short trips around town, but do it while fully warmed up.

Read up on everything from @jonheld since yours is a 92, it has the 3FE.

 

[jonheld]

For a reference point, in the 25 years I have owned my 91, and the countless times the battery has been disconnected/reconnected, I have NEVER had a "rough idle" after installation. Usually the idle will be higher than normal for a few start/drive/stop cycles. It behaves exactly like my 97 in this respect.

A rough idle on a 3FE is almost always attributed to a vacuum leak or unmetered air entering the system.
It is very unlikely that the fusible links would cause this, however I change them with every battery replacement. The OEM set of 3 will set you back a whole $15 from Wits' End, Solutions for Problems You Didn't Know You Had or any of the online OEM retailers out there.

I strongly recommend that you read through this thread regarding basic tune-up parts for your truck. With very few exceptions, all OEM parts are still available, and you should make every effort to keep the entire ignition system OEM.

General 3FE Tune Up Info

This now lives in the Resources section in this forum. Most info is 3FE specific, but the basic idea applies to any vehicle. *****NOTE***** As of 3/2019 the EGR Valve: OEM part# 25620-61120 is NLA. This is in response to "my 3FE has no power" or "I just bought a 30 year old truck and it's not...

forum.ih8mud.com

 

[DesertCruiser80]

Thanks for the Tune up info @jonheld. I've been working my way down that list. Next on my list is to check the EGR valve. (That damn nut on the hose is really tight.)

On your '91, did a battery change not reset the ECM like @BILT4ME suggested? Or is that of no importance? What has me confused is that I thought I solved the rough idle when I gapped the plugs.

 

[BILT4ME]

Thanks for the Tune up info @jonheld. I've been working my way down that list. Next on my list is to check the EGR valve. (That damn nut on the hose is really tight.)

On your '91, did a battery change not reset the ECM like @BILT4ME suggested? Or is that of no importance? What has me confused is that I thought I solved the rough idle when I gapped the plugs.

If @jonheld said it, it's correct.

 

[jonheld]

Thanks for the Tune up info @jonheld. I've been working my way down that list. Next on my list is to check the EGR valve. (That damn nut on the hose is really tight.)

On your '91, did a battery change not reset the ECM like @BILT4ME suggested? Or is that of no importance? What has me confused is that I thought I solved the rough idle when I gapped the plugs.

Removal of power from the ECU for a period of time by removing one or both battery terminals (doesn't matter which) or removing the 15 amp EFI fuse in the fusebox will "reset" the ECU. This will clear any stored error codes, and force the ECU to "re-learn" the sensors. It is similar to rebooting a computer.
So the short answer is yes, it did reset the ECU, but I have never had rough idle due to an ECU reset. There is something else in play here.

 

[flintknapper]

For a reference point, in the 25 years I have owned my 91, and the countless times the battery has been disconnected/reconnected, I have NEVER had a "rough idle" after installation. Usually the idle will be higher than normal for a few start/drive/stop cycles. It behaves exactly like my 97 in this respect.

A rough idle on a 3FE is almost always attributed to a vacuum leak or unmetered air entering the system.
It is very unlikely that the fusible links would cause this, however I change them with every battery replacement. The OEM set of 3 will set you back a whole $15 from Wits' End, Solutions for Problems You Didn't Know You Had or any of the online OEM retailers out there.

I strongly recommend that you read through this thread regarding basic tune-up parts for your truck. With very few exceptions, all OEM parts are still available, and you should make every effort to keep the entire ignition system OEM.

General 3FE Tune Up Info

This now lives in the Resources section in this forum. Most info is 3FE specific, but the basic idea applies to any vehicle. *****NOTE***** As of 3/2019 the EGR Valve: OEM part# 25620-61120 is NLA. This is in response to "my 3FE has no power" or "I just bought a 30 year old truck and it's not...

forum.ih8mud.com

^^^^ Spot on . 'Rough idle' is something different than the ECU 're-learning' the idle after battery disconnect. I've had mine rev up (high idle) as high as 2,000 rpm after battery disconnect but never 'rough'.

 

[cruiserdan]

It's something like 30 stop/start sequences. Not about how long, but most start it and drive it on short trips around town, but do it while fully warmed up.

Read up on everything from @jonheld since yours is a 92, it has the 3FE.

To clarify:
Low curb idle after power interruption happens to 93-94 1FZ variants. The idle re-learns usually within 5 to 10 key cycles. To fast track it start the truck and let it warm up til it comes off fast idle. Shut it off and restart after about 10-15 seconds. Let it run until the idle stabilizes (usually less than a minute) and shut it off. Repeat the process a few times and you will see the idle come up a little each time.

 

[BILT4ME]

To clarify:
Low curb idle after power interruption happens to 93-94 1FZ variants. The idle re-learns usually within 5 to 10 key cycles. To fast track it start the truck and let it warm up til it comes off fast idle. Shut it off and restart after about 10-15 seconds. Let it run until the idle stabilizes (usually less than a minute) and shut it off. Repeat the process a few times and you will see the idle come up a little each time.

Thank you Dan!