1991 Isuzu Trooper idle problem

1991 ISUZU TROOPER
236,000 MILES
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CSJETER
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Won't maintain idle.
Replaced timing chain... in process replaced push rods lifters. Cylinder head machined prior to chain going. During troubkeshooting replaced all sensors and properly adjusted tps.
Replaced both fuel injectors.. to no avail replaced computer. Problem continues to exist.
Oct 21, 2013 at 7:14 PM
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JACOBANDNICKOLAS
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Have you checked for vacuum leaks? Have you checked the idle air control valve?
Oct 22, 2013 at 5:24 AM
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CSJETER
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Yes.. it appears to be a vaccum leak but am unable to locate. The following have been done:
After replacing timing chain had to replace push rods, lifters, cyclinder heads machined, replaced all sensors incl. TPS (which were properly adjusted), changed IAC, replaced computer, TBI, rebuilt fuel pressure regulator, repaced intake manifold gaskets, throttle body gaskets. Checked all vaccum hoses... could not find leaks. The vechicle does not maintain idle after reaching operating temp... idle drops.struggles between 2-5rpms. Currently in the process of replacing coil.
Please advise as what else I may overlooked.
Btw: recently found the accelerator screw. It appears to be rusted and is currently a little hard to move.
Oct 29, 2013 at 10:33 PM
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JACOBANDNICKOLAS
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I don't feel the coil is the problem. When checking for a vacuum leak, have you used something like carb cleaner?
Oct 30, 2013 at 4:58 AM