A seemingly unconquerable problem

[Atom Eyes]

My one-owner '89 K5 has 173,000 happy miles on its original TBI 350/700R4 drivetrain. Aside from my ongoing rusty body panel replacement program, for the past couple of months I have been experiencing a really irritating hesitation/rough idle problem which was so bad at one point that the truck was virtually undriveable, a radical departure from its normal silky-smooth, fast accelerating history. First, I did a full tuneup, adjusted the timing and replaced the EGR valve and fuel filter. A slight improvement. Then one spark plug was found to be cracked and was replaced. When she started acting badly again, some vacuum lines were replaced. This finally alleviated the rough idle. Again, she was okay for a couple of days until the exhaust pipe (I still have a single exhaust, can you believe it?) was found to be rusted from the cat back and was replaced. I figured the hesitation came from a backpressure problem and was surely solved now, but it still persists. I don't know what else I can possibly replace now. Any ideas?

 

[ryan22re]

Check fuel pressure. And for vacuum leaks at the intake/throttle body. Any codes coming out of the computer?

 

[1985_K5_Silverado]

Definitely check for trouble codes and hook up a vacuum gauge to see if the needle does anything unusual. Ditto on the fuel pressure as suggested some moments ago by my distinguished colleague.

 

[4X4HIGH]

Did you disconnect the EST wire when you timed the rig? Also fuel pressure check should help alos like was already said. It is possible for the fuel pump to be dying on you after that many miles. Mine was having similiar issues and once i replaced the fuel pump troubles were gone.

 

[cutlass350]

When you did the tune up did you put on a new cap and rotor? I went through all the same things at about 130,000 miles and my dumb ass didn't replace the cap. One day I washed my truck and it ran so bad it wouldn't even pull out of my driveway. Once I replaced the cap it obviously ran much better.

 

[DEMON44]

I'll bet your catalitic converter is plugged near solid...if you have one.