Guys, I have read several posts here regarding idle fluctuations and engine stumbling under load. I am having the same problem and I have done darn near everything I know to do except replace the intake manifold gasket(and I really don't want to have to do that). Below is a list of things done to the '90 Trooper w/2.8 six cylinder:

New fuel filter
New plugs & wires
New distributor cap and rotor
New coil
Timing checked
Checked egr valve
New O2 sensor
Seafoam poured directly into the throttle body and into fuel tank
Disconnected Temp. Sensor (made no difference)
Attempted to check vacuum hoses although I really didn't find very many

What am I missing other than the intake manifold gasket?

Any ideas?

to see if it is your intake manifold gasket, spray some carb cleaner or starting fluid around the gasket. If the rpm's go up then you know it is the gasket.

TB-

I changed the title of your post to better reflect the subject of your question. I know you are frustrated, but you need to use an appropriate title that describes what you are asking.

BTW, the intake manifold gasket could be your problem, but don't get it mixed up with the intake manifold gasket problems the newer 3.2 have. Just making sure you are reading correctly.

Good Luck,
Michael

check and clean IAC motor

disconnect vacuum hose from MAP sensor, and plug the hose with your finger. if it behaves about the same or better than with MAP sensor connected, go to a junk yard and pull the MAP off about any similar-year chevy product and use that. You can probably go by the pocket rule at the junkyard and have a clean conscience, as chances are 99.9% that the sensor in your pocket would have just been crushed and burned with the rest of the stuff nobody ever buys.

if the above two don't help any, thoroughly check over all vacuum connections repeatedly and replace as many as you can. hose and connectors are *relatively* inexpensive, and worth doing on ao 10+ year old truck. don't forget the ones under the dashboard that go to the HVAC controls. (and are a pain in the you know where to replace! <img src="/forums/images/graemlins/angry.gif" alt="" /> <img src="/forums/images/graemlins/angry.gif" alt="" /> )

Good luck! <img src="/forums/images/graemlins/kewl.gif" alt="" /> <img src="/forums/images/graemlins/cheers.gif" alt="" />

You can probably go by the pocket rule at the junkyard and have a clean conscience, as chances are 99.9% that the sensor in your pocket would have just been crushed and burned with the rest of the stuff nobody ever buys.

Wow, Eric, I have seen some creative justification before, but that really takes the cake. Is the 5 bucks any semi-respectable yard going to charge you not worth a clear concience? <img src="/forums/images/graemlins/smile.gif" alt="" />

Michael

would it sound better if I said it like this?

9 times out of 10, when I go to the yard and pull of some dinky little part like seat belt retainer, clip thingie from a throttle cable stop, window crank knob, IAC motor, whatever... basically anything that fits inside one hand - when I plunk it down on the counter they tell me not to worry about it and have a nice day.

(they make enough money selling me big parts, I suppose <img src="/forums/images/graemlins/shiner.gif" alt="" /> )

would it sound better if I said it like this?

Much better. <img src="/forums/images/graemlins/smile.gif" alt="" /> The choice to charge/not charge is theirs, not yours or mine. It would be like someone walking into your garage and liberating some of the tools you don't use much because they *thought* you would not miss it.

I may not like "Auto Recyclers", but that does not mean it is OK to resort to their level by thieving things from their lot.

Michael

Purchase a re build kit for your TBI. It will have new gaskets,o-rings,injector filters,and most important, a new diaphram for the fuel pressure regulator. I had this problem on my 92 2.8 rodeo and I checked all the same things you did, the kit did the trick.

Bought TBI rebuild kit, installed it and zero change. Sprayed starting fluid at all hoses, apparently no leaks. As suggested, removed vacuum hose from MAP and idle went down to normal and jumped to 1,500 RPM when reinstalled. Don't know how it would have performed on a road test.

Idle still fluctuates wildly, engine still stumbles when under load. Boy, this is becoming very frustrating.

http://cgi.ebay.com/ebaymotors/ws/e...p;category=33557&item=2448174663