My 1988 Isuzu Trooper does not idle right. When I am stopped, the engine revs up and down and so forth until I start going again or shut it off. It is a 2.6L S model with 5speed and 4X4. Also when I shut it off, it will not start right up again until it cools down a bit.

Perhaps a dirty fuel filter, dirty injectors, condensation/water in the fuel, dirty air filter. Pretty much tune-up related items hopefully. Could be a host of other problems, however, you need to start somewhere.

Kinda sounds like a vacuum leak to me...can't help much more than that though.

I put a new fuel and air filter on not that long ago. I am planning on putting in new injectors soon. I am also planning on having our Isuzu dealer get in and communicate with the computer.

It's an '88. You don't need a dealer. I am actually surprised you even have a functional dealer left.

Under the center console should be the ECM. With it are two single wires. Plug them in, turn the key to on and count the flashes of the Check Engine light. It will start with 12 (flash-pause-flash-flash) and then spit out any codes in the same fashion and then will end with 12 again. If all is good, then all you will get is 12.

I agree with BigSweed above, it sounds vacuum like. Either you have leak(s) on the many vacuum lines, or the vacuum valve on top of the thermostat housing is not working properly.

Is it overheating? Is the coolant full? Does the coolant look normal? These engines will bump up the idle if they get hot, but they can also do it if there are bubbles in the cooling system from either a leak, low coolant or a head gasket issue.

Good luck,
Michael

I checked the ECM. All it gives is a 12. The vacuum valve on the thermostat housing is new since my old one was old and a couple of the hose hookups broke off. The vacuum lines may be the problem. It isn't overheating and I just recently had to replace the heater hoses so I replaced the coolant. The coolant is full. There are no bubbles. The dealer up here in Alaska is a Volkswagen, Porsche, Audi and Isuzu dealer.
www.morrisonautogroup.com
I have replaced the PCV valve, Thermal Vacuum Valve, Heater Hoses, some vacuum tubing, coolant, battery, fuel and air filters. I don't know if this may be a problem, but it no longer has an air pump on it.

If you've done that, I would look at three things, next.

1) O2 sensor. These things idle like crud when they go bad.
2) The rest of the vacuum tubing. Especially the stuff under the intake manifold that is nigh impossible to get to.
3) Compression test. The 2.6 will run amazingly well with bad valves, but it will not run quite "right".

Good Luck,
Michael

(Another option is the IAC valve under the intake manifold. It produces strange symptoms when it is not working correctly and if it is sticking open a bit, it will give a vacuum leak condition.)

My Dad and I did a timing check on it. BAD! I checked the compression, BAD! So we pulled the valve cover off and put it in TDC. When in TDC, the valves aren't right. We pulled the front cover over the timing belt. The CAM sprocket is off time by about 90 degrees. We are in the process of fixing this problem now. Then we are going to adjust the distributor correctly and see what happens. I will update this a little later.

JFYI The outer hub on the crank pulley is known to rotate out of time. If you pull the pulley off the mark should line up with the keyway slot.




Jim

It isn't that, is just when you rebuild the engine and you line up the tabs and marks on the cam sprocket for the timing belt, it isn't lined up right now and the crank is in TDC. The crank pulley is ok. The reason I have bad compression is because when the engine is on the compression stroke, the valves aren't in the right place. The cam is what is off time.