What you are describing sounds like something that could also be caused by a bad throttle position sensor. It's on the passenger side of the TB unit and moves with the throttle plate. Very easy to replace and relatively cheap, about $30 at AutoZone. AutoZone probably also has a tester if you take yours off and bring it in to test.
I'll pull it off sometime this week and take it to have it tested. Thanks for the tip; I'll report back when I have news.
Another thing you can try as a diagnostic is to pull the vacuum feed for the EGR off at the TBI and plug the port on the TBI. On my 89 4.3 the whole bunch of junk that controls the vacuum to the EGR seemed to have a vacuum leak of some kind and the truck ran a lot better with it capped of as I described. It will cause the computer to set a code if you drive it for more then about 15 minutes as the ECM purposely "exercises" the EGR about every 20 minutes to see if it's working. I followed the factory manual to try and pin down whether that EGR controller was bad or not and according to the tests it's OK yet it still seemed to allow too much of the vacum to get out causing the truck to run lean and stumble. I eventually "fixed" it by inserting a plug in the vacuum line with a very tiny pinhole thru it to allow vacuum but only allowing small amounts of air to move thru it to stop the "leak" effect. IT's enough to stop a code from being set.
On a similar subject: Is there a way to prevent the "delayed return to complete idle feature" since this wastes gas? Thanks. brody
Wastes gas? You're kidding right?
Doc
Nope. When you decelerate in a lower gear you can clearly feel the IAC take several seconds to completely reaach full idle. IMHO that's using extra fuel. Something to do with smog control I think. Maybe it's only installed for certain states. brody
I know of what you speak. I was asking if you were kidding about the "wastes gas" conmment. The "extra" amount of fuel used, if any, is negligible as the engine isn't under load and very close to idle RPM.
Doc
I'm glad that you understood what I was talking about. But when you consider that every time that you take your foot off the pedal the same thing happens it must add up to a considerable waste of fuel. I got into the habit of shifting into neutral every time I release the throttle, figuring the IAC would immediately go full idle. I have an old Mazda that had a dash-pot diaphragm that did the same thing so I removed it and now it goes to full idle immediately. What the hell, why pay the oil companies that extra squirt? :-) brody
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