Occasional Rough Idle - Toyota Nation Forum : Toyota Car and Truck Forums

BobThib · 01-25-2011, 05:33 PM

My was was coming home from work the other day and she called all a tizzy. The car was "bumping" at a red light. What she meant was that there would be an occasional hiccup in the idle while she was stopped. She described the sensation similar to what happens when you are filling the tank with the car running. (I know, don't tell me.) It starts to idle very rough, but then smooths out.

I had a chance to drive the car today. It started great and accellerated smoothly. I went about a mile and stopped for a light. The car was still warm from her ride home a few hours earlier, and the temps outside was mid 70s. The car did hesitate and "bump" a few times at the light. Idle was about 900 rpm, but drop to about 600 when it hesitated.

The car accelerated smoothly from the light, and I drove in 12st, 2nd, and 3rd manually (its an automatic) and had no problems with misfire or hesitation. It acted normal on the road, but still hesitates now and again at a stop light.

She put in some STP gas treatment at my request right after the first incident. That has not seemed to help.

Anyone got any ideas? A friend who is a boat mechanic said it might be the idler valve.

Phlingwinger · 01-25-2011, 06:57 PM

My 98 Rolla used to do that (only when my foot was off the accelerator) until I replaced the accessory drive belt. Turned out that when the air conditioner compressor clutch would engage it would momentarily slip the belt, and the engine would bog, then recover just before a stall would happen...

So...are you running the A/C, and is your drive belt old?

Phlingwinger

BobThib · 01-26-2011, 04:35 PM

Quote:

Originally Posted by Phlingwinger

My 98 Rolla used to do that (only when my foot was off the accelerator) until I replaced the accessory drive belt. Turned out that when the air conditioner compressor clutch would engage it would momentarily slip the belt, and the engine would bog, then recover just before a stall would happen...

So...are you running the A/C, and is your drive belt old?

Phlingwinger

PH, we live in FLA. We run the A/C 98% of the time. We'll take it out tonight, (low 70s) turn off the ac roll down the windows and cruise. We should know tonight if that is it. Thanks!

BobThib · 01-26-2011, 04:37 PM

Quote:

Originally Posted by hummerh2o

Check your spark plugs, i would have a horrible idle at red lights until i changed those out.

Hummer, we're going to try driving with the ac off tonight. If that's not it I'll swap out the plugs tomorrow. Don't remember when they were last changed. Thanks for the idea!
BT

Phlingwinger · 01-26-2011, 07:16 PM

Right on Bob,

Try running her on the Sawgrass and take an off ramp with a downhill so you can get off the accelerator early and brake hard. I always had my worst bumps occur climbing off of 595 onto SR84 or when I would come off 75 onto Royal Palm in Weston (stop signs or stop lights shortly after 70 MPH)...

BobThib · 01-26-2011, 08:05 PM

Ph, we just got back from a spin with no ac and it still happend. My wife said it's been much better the past day or so. We filled the tank and added STP and I think it might just be some bad gas. We'll keep an eye on it.

Thanks for the ideas. BT