Ever seen this? Low idle and dash warning lights. (1 Viewer)

[rbryan]

my idle sits right at 650 for a few minutes but then slowly starts to drop down to about 550 - this isn't the new part. What is new is that now when the idle goes under about 600 the A/T Oil Temp light, the Break light and the Battery light all come on. Once I start to drive or just rev the engine, the lights go off.

Thanks!

 

[TCH2FLY]

We need a bit more info on the truck to help with the idle issue.. year, mileage etc.
The other issue is related, the electrical system is setup to illuminate all those lights to indicate the alternator is inop, in this case it is because of the low idle. That is why they go off when you rev the engine.

 

[jvazquez53]

We need a bit more info on the truck to help with the idle issue.. year, mileage etc.
The other issue is related, the electrical system is setup to illuminate all those lights to indicate the alternator is inop, in this case it is because of the low idle. That is why they go off when you rev the engine.

I had the same problem and it was not the alternator, the idle would go down so much that the truck would quit. My mechanic did something which I don't know but tomorrow I'm going to see him and ask him.

 

[CJF]

the A/T Oil Temp light, the Break light and the Battery light all come on.

Standard low voltage warning.

Alternator likely going out. Of course could also be a loose battery connection, etc.

 

[rbryan]

Thanks Jose, I'm very interested to know what he did.

I think it is directly tied to getting the idle correct. The funny thing is the idle has always started right on and then lowered but the lights never came on. I replaced the alternator about 6 months ago, had the battery checked this weekend - everything is working fine. Maybe a belt needs to be tightened but not sure how that would impact the idle?

 

[rbryan]

We need a bit more info on the truck to help with the idle issue.. year, mileage etc.
The other issue is related, the electrical system is setup to illuminate all those lights to indicate the alternator is inop, in this case it is because of the low idle. That is why they go off when you rev the engine.

It's a 91 with a 3fe. Mileage is somewhere between 130k and 330k, carfax showed 300k as last service before someone changed the odo. I bought the truck knowing that it was a work in progress.

 

[TCH2FLY]

Thanks Jose, I'm very interested to know what he did.

I think it is directly tied to getting the idle correct. The funny thing is the idle has always started right on and then lowered but the lights never came on. I replaced the alternator about 6 months ago, had the battery checked this weekend - everything is working fine. Maybe a belt needs to be tightened but not sure how that would impact the idle?

I may have been too specific but (as CJF more clearly stated) the lights indicate low voltage and that usually means the belt broke or for some reason the alternator is weak/inoperative (meaning not enough output).
With your low idle the system thinks the alternator is not working correctly and the lights come on ... idle goes up, lights go out. I think correctling the idle will solve your issues here. (yes double check the belt tension)

It's a 91 with a 3fe. Mileage is somewhere between 130k and 330k, carfax showed 300k as last service before someone changed the odo. I bought the truck knowing that it was a work in progress.

Aside from the alt replacement, any other work prior to the low idle issue? I assume the check engine light is not on but have you check for codes?
On an older truck I would suspect a vacuum leak so check the air intake hose first and then make sure all the vacuum lines are in place.

Good luck, let us know what you find

 

[prichard]

Did you get a chance to diagnose the problem? It looks like I'm having the same issue.

 

[rbryan]

Did you get a chance to diagnose the problem? It looks like I'm having the same issue.

I haven't yet, hopefully this weekend. Will let you know what I end up with.

 

[guzzla]

A mate of mine spent ages trouble-shooting a low idle issue. It ended up being a very small crack in the air intake pipe going from the air cleaner to the throttle body. It's worth checking and very closely too. A small crack can be really hard to find on that convoluted intake pipe.

I never had any issues but I decided to check mine just to be sure. I removed mine and it had some suspect cracks but they cost a fortune to replace with OEM here. So I filled all the groves with Sikaflex sealant then reinstalled it and allowed it to dry

 

[ShawnTRD]

It ended up being a very small crack in the air intake pipe going from the air cleaner to the throttle body.

Easy way to test this is spray the vacuum lines and intake tube with WD40 or Start Fluid. If the RPM raise it's because it sucked in the WD40 or Start Fluid.

Also is this when you just sitting at idle? My old Tacoma would drop to a very low idle then coming to a stop. It was my MAF sensor. It was dirty from a POS K&N Air Filter I had. I've also see similar problem from tranny fluid being low. But that was in a Ford.