this culd be a few things i had this problems and it was the connectors on top of the injectors were lossing contact with the injectors,then i have seen the weights in the dist not advancing the the timing interally.

 

How can you tell if the connectors on the injectors are the problem? Both injectors are spraying but that is all I can tell. The old distributor was doing the same idle problem so I guess it won't be that.

Thanks for the ideas.

 

Well, if you've eliminated Fuel, Spark, and Air as possible issues you're not left with much to work with are you....here's a few ideas to try:

* Spray the distributor with water from a spray bottle while the engine is running.....see if it's arcing ouside the cap (possible, but not probable)

* Spray down the entire intake manifold with carb-cleaner while the engine is running...if there's a vacuum leak you'll know about it right away

* Pull each vacuum hose one at a time, cap the fitting, and see if the idle improves...

* Check the TBI throttle plate shaft for wear...if it wears the TPS will still function but you'll get an air leak around the shaft and plates due to mis-alignment in the bores (this is a COMMON TBI problem.....but one that usually gets overlooked or mis-diagnosed)

* Try using an external fuel source to diagnose fuel line/pump/tank problems....most race shops or dyno places will be able to help you rig this up to test....

* Have you changed the ignition module ???....just because the dist. was changed doesn't mean the ignition module was too....

* You said this was a GM crate motor, is it stock displacement and compression...and is the cam at stock specs ??

* was the TBI put back together right when the fuel pressure regulator was changed (it's pretty easy to change...but you CAN screw it up)

* What's your plug-gap set at ??

That's all I can think of right now....

 

The ignition module was changed twice. I will check the arcing. The tbi housing is new but could be something wrong. I do not know how to check the blades. I have never completely tore one apart. The engine is a GM stock replacement. It is a commonly sold engine. The dealer does quite a few and sells about 10 a month so it must not be a problem with the engines. I had the same problem in my old stock engine though so it has to be something else. The gap is set at the factory specs under the hood. I can't remember what that is right now. It has been awhile since we did the plugs. That was at the beginning of the mess. There doesn't seem to be an vacuum at the port that goes to the vapor canister from the tbi. Is there suppose to be. The idle is high and the vacuum readings were high at one point.

 

CHANGE THE SPARK PLUGS !!!.....you may have fouled them out somehow awhile back and not noticed it, try regapping them to .030" too (.035" is stock I think), this "might" be your whole problem....a marginal plug might work fine under moderate/hard acceleration but at idle/light throttle it'll misfire like crazy !!

Vacuum to the vapor canister is throttle regulated if I remember right.

High idle indicates a vacuum leak....try the carb-cleaner on the intake manifold trick.

Does your gas-pedal ever feel "sticky" or feel like it's got a "dead-spot" in it ??...this can be an indication of throttle-shaft bushing wear.....

 

any progress?

 

I got sick and haven't been able to do anything. I have another car I just bought that is having problems after a pinion seal replacement at the dealer so I have been and am still trying to get it fixed.

The throttle doesn't seem to be doing anything different. In md throttle range around 40mph it has been having no power like it was bogging down but now it is shaking the truck when you do this. Also it has started pinging especially going up hills. I talked to the mechanic and he acted like he wants me to drive it until it breaks down so he can figure it out. I have to get the pinging fixed because I am not going to mess up the new engine. There is also a noise under the truck where the area of the torque converter that sounds like something is off balance and vibrating and making a dull noise you can hear when you are at the truck or walking away.

When you press the brake pedal the idle gets really unstable too. When you shift the gears from park to neutral to drive it gets really bad too.

The docter says it will be 2 more weeks before I am well enough to work on it so I will let you guys know if anything happens.

 

Where is the throttle shaft bushing? Is that in the tbi?

 

I would bet you have a vacuum leak somewhere. Brake booster, VAC canister, dist, somewhere.... start checking vacuum lines

 

the throttle shaft bushing is the plastic bushing that the shaft holding the throttle plates in the TBI rides on....

From the sounds of it though I'm beginning to believe it's a BIG vacuum leak like BlackGMC said