For 2 years now I have been experiencing an intermittent hesitation. All speeds, but just when maintaining a steady speed or when just letting up on the gas. Actually, lately it is becoming most noticeable when the engine is cold, but not right away. It hesitates after being driven about half a mile, but way before it warms up. When this happens the idle, normally 950, gets unsteady, going from 1200 down to 800 and back. One temporary cure, whenever it does this hesitation, I have found, is to rev the engine to about 3000 RPMs for a second or two. This will stop the hesitation for a random interval of a few minutes up to a day or two. 78,000 miles, non-turbo, all new plugs, wires, rotors, etc. and a new MAF. I have been waiting for it to get worse so it can be diagnosed as it doesn't throw any codes. 2 Indies and a Dealer have not been able to figure it out. I have reviewed years of this Forum's topics and see no solution offered so far. The plan now is to begin replacing all parts, probably starting with the TPS. I would appreciate any thoughts anybody may have and recommendations as to the possible best sequence of remove & replace, or any other thoughts.
Thanks in advance for any input.

Remove the hose from the air cleaner to the throttle body and inspect it for tiny leaks in the accordion section. Even a pin hole will make a diffference.

My intake hose was not tightened enough. my fault. When I took it for a test run today, I added a little turbo boost at about 35mph and hear a "pop" sound from the engine. It wouldn't go over 40mph and idle was erratic. The "pop" was the intake hose popping off under pressure. No CEL.

Klaus
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1975 164 w/174,800mi (Sold) 1995 850T w/91,000mi, 1998 V70R w/129,000mi

TPS ok but out of position? Throttle body dirty, loose, or misaligned? Hoses to idle air motor (or other vacuum hoses, such as brake booster) leaking or shifting time to time (as motor shifts under torque/acceleration)? Someone tampered with stop screw on throttle body? Unrelated glitch in voltage regulation?