Gents,

I've been scratching my head about a mildly annoying issue with my '89 Runner V6 3.0. It is one of those infrequent glitches that only occurs under specific conditions.

Some background:

When I leave work, and it is cold (in CA that is 40 F at 5:30 at night) I coast down a hill in second gear with the throttle at idle, to stay under the 25 mph speed limit on my work site. The idle will surge up, down, up, down about 800 RPM. The truck responds to this surge with a mild lurching. If I put a little throttle into it, it goes away. After it is warm, never occurs.

Things I have checked:

I have checked and rechecked the idle position sensor.
I have looked high and low for a vacuum leak, spraying starting fluid around connections, etc.
I have checked all of my electrical connections, they are tight.
All of the plugs, wires, cap, rotor are new, less than 5k miles.
Injectors were cleaned/rebuilt last spring when I rebuilt the motor.
Valve adjustment done a month ago, three valves were slightly out of range, shimmed them back in.

I do hear an exhaust leak somewhere and have not tracked it down yet.

Opinions?

Thanks,

Mike

When you had the injectors cleaned, did that include the cold start injector? Maybe if it were leaking, that could account for it.

Yup, sent the cold start injector off for service as well.

Good suggestion.

Thanks,

Mike

Check your intake boot for cracks. You might need to remove it to fully flex it and look in between all the ribs. My 88 had the weird surge issue your describing.

I couldn't find a 3VZe intake boot at the u pull it so I got one off a 93 Acura that fit, idle settled to 950 and smoothed out after that.

Also check / burp the coolant.
Sometimes a little low on coolant can cause this too.
At least on a 22RE.

Good point on the intake boot. I had to replace the boot that comes off the throttle body, as it ripped one day when removing it. It is only 8 months old. Those things are not cheap.

I will check the two way boot that comes off the AFM.

As for the coolant, I will look at that also, have not checked it lately.

Thanks gents,

Mike

Quick way to determine the problem - duct tape. If you have a leak, wrap the thing and see if it goes away.

Just thought I would post the solution to the problem.

Culprit ended up being a coolant system that needed to be burped. Did it once on a good incline, had to add a fair amount of fluid. Did it a second time a few days later, added a bit more. Why this would cause the problem, I can only guess. But, I will take lucky over good any day.

Has not done the surge thing since then.

Thanks gents,

Mike

Air in cooling system can get under the ECU coolant temp sensor. Air will read cooler than the coolant and the ECU "thinks" the engine is cold and so goes back to the cold start / fast idle mode to get the engine up to proper temperature.

Ahh, makes sense. On the 3VZE there is a sensor block on top fof the intake manifold, back of the motor, by the firewall. This is one of the highest points in the cooling system and from what I recall when I had it off, would be prone to having air trapped in it if the coolant was low.

Thanks Roger,

Mike