high/hunting idle

[T Jay]

Hello Folks,

My '88 Trooper has developed a high and sometimes hunting idle, and it started a few weeks ago when the weather got colder here in the Northwest. It normally idles at 900 rpm at a stop, but now it's in the 1200 to 1700 range and sometimes hunts in between. The other day the outdoor temp was in the 60's and Trooper was back to a 900 idle. Now the temp is in the low 50's and the high idle is back.

Any thoughts? Vacuum leak? A sensor of some kind? Radiator issue?

The fuel and air filters are new along with the plugs, wires, distributor, cap & rotor.

I am also noticing a slight loss of coolant.

Thanks Much,
Tony

[mmPriest]

No knowledge on the 2.6 but if it were a sensor causing high idle it could be either a TPS(Throttle Position Sensor) or a Engine Coolant Temperature Sensor. Have you sprayed your vacuum lines for leaks yet?

[Trooper2Guru]

glad you asked that question because i am having a similer problem and for the life of me cant figure it out. it has almost got to the point that a match is going in the cab !!!!!. if you get anything figured out i would sure like to know.
thanks and good luck.


Tommy

[ga trooper]

On my 88 trooper and on the 92 Amigo I have noticed the vacuum lines leading to and leaving the temperature valve on the top of the thermostat housing split due to old age and causing the same prob. If I understand the operation of that valve it opens once water temp reaches operating temp and allows air to pass to vacuum switching valve (VSV) and if temp gets too high it will open essentially a vacuum leak to allow the engine to idle faster to cool off. All that said if the hoses are leaking it will idle fast due to vac. leak at the wrong time and place. ie. not thru the mass air and truck don't know what to do. This fixed mine. Trooper2Guru, does this mean i get your truck now? If my theories of operation are wrong, Jerry please correct me!

[isuzufool]

Same symptoms on my pickup along with the loss of coolant eventually led to a total failure of the head gasket, and warped head, and burnt all 4 exhaust valves. But that's a worste case cenario I suppose.

Look into that thermal valve on top of the thermostat housing. You can actually eliminate it if need be.

[CHW2021]

Try to check the mass airflow sensor, I am not familiar with your engine but, the airflow sensor can cause a hunting idle.

[isuzufool]

Not likely, but I would start with checking for any kind of vacuum leak first. Then that coolant loss still concerns me, but not if you can see where it's leaking from versus the engine consuming it! More details please!

[MarkB.NV]

The high idle issue is prolly due to a vacuum leak, or a malfunctioning thermal valve
or the fast idle seloniod. This is based on my novice understanding of the vacuum and
emission system ... so bear with me, heh heh.

There are two things that can effect this, the Aux Air Valve, and the Fast Idle Selonoid.

You should be able to test these and find out which is leaking and causing the problem.
There is a good thread here with pics to help find your way

Linky ==> http://forum.planetisuzoo.com/viewtopic ... ght=plenum



So, when you're driving the truck and it is having the high idle problem ... stop and make the following tests:

1. Remove the bottom hose from between the thermal valve and the plenum (plenum is sometimes
called the intake manifold common)- BE SURE TO BLOCK off both ends -the hose and the thermal
valve and not make more leaks. Did the idle change? This could account for the fast idle when warm.
If the idle doesn't change, then its prolly not the thermal valve.

2. Repeat the same test with upper hose on the thermal valve that goes to the Fast Idle Selonoid.
BE SURE TO BLOCK off both ends. Did the idle change? This could account for the fast idle
when warm. If the idle doesn't change, then its prolly not the fast idle selonoid.

3. Check the all of the hoses running to the other vacuum switching valves. If these are leaking they
would cause a fast idle, but prolly would not account for the warm/cold difference you mentioned.
One of these gets told by the ECM when to suck vapors out of the charcoal canister, and the
other gets told to modify the fuel pressure during high RPM.

4. There is also a possibility that its the aux air valve under the intake manifold - but I haven't
figured out an easy way to test that and don't have the FSM.

Report back and lets see what we gots.

[MarkB.NV]

Also, when my 2.6 had a surging problem, it was caused by a bad O2 sensor.
Easy to test that, even the chiltons manual had a test procedure using a meter.

[RicksVX]

Hello,


Mine had a similar issue. After replacing all of the vacuum lines, the spark plugs, cap & rotor, wires, filters, etc., I discovered it was the top butterfly on the air intake hanging up slightly. I think it is because I tightened that clamp for the intake a bit too much. Anyway, I spent some time working it with some PB Blaster on the shaft and some emery cloth in the passageway. That did it! Any time it starts to act that way again, I just squirt a little PB Blaster on the shaft and spring assembly and it stops.

I also had some surging at speed. One (hot) day, the fuel pump failed. I replaced it and that fixed the surging.

Good luck!


Sincerely,

Rick

[Marsh]

Someone else posted this in a response on another thread:

"Sounds like the auxiliary air regulator (the round thing under the intake manifold) is giving you fits. Try unplugging the connector and see if it makes any difference. It's a Bosch-style 2-pin connector, the rear-most one on the bottom of the intake. There is a hose on the bottom that is U-shaped to connect to the intake manifold.
It is designed to bypass the throttle body to allow more air when the engine is cold. It has a bi-metallic strip that is attached to an electric heater. When cold (and engine off) it allows maximum air into the engine to assist cold starting. As the engine runs, the heater heats that strip and causes the valve to close. It takes a minute or so to close completely. If the valve is messed up, then it could cause your issue.
You can clean that valve by removing it, loading it full of a penetrating cleaner (PBBlaster comes to mind) and let it soak for a couple of hours, and see if you can break it loose."

My auxiliary air regulator ("AAR") caused me to have the exact problem that you described during cold weather. Instead of buying another $150.00 AAR and enduring the skinned knuckles and cursing that replacing it caused me in the past, I bought a simple heater valve from the local NAPA store, cut the air hose connecting the AAR to the intake manifold and installed the heater valve in the line. My Trooper now has its hot weather idle speed of 900 rpm, when warmed up with the heater valve in closed position. The idle with the valve closed, when it's really cold, doesn't fall below 500 rpm. If I ever wanted to get a faster idle during cold starts in cold weather without opening the hood, I would rather install a manual choke cable to control the heater valve than purchase and install another AAR.