My 92' 350 B4C has acquired an eratic idle and also at cruise. Anyone have any ideas. There are no codes stored and no service engine soon light. It sounds like a TPS sensor but there are no codes. I am just wondering if anyone would have a real good idea on it. Otherwise the car runs excellent. Thanks in advance for any suggestions.

 

92,

What have you done to the car for maintenance so far? (Plugs, wires, etc.?) I had a similar complaint on a TPI that I fought for a couple of seasons. The car ran fine above 1,700 RPM but wouldn't idle smoothly for squat. The idle didn't wander, but it always felt as if there was a miss. I check plugs, wires, cap, and rotor several times. I tested the reluctor, inspected valves, tested compression, measured cam lobe lifts with a dial indicator, checked for vacuum leaks at the runners, intake, plenum, throttle body, PCV, etc. Tested fuel pressure and leakdown, and never found the problem. I finally performed a power balance test with a known good ignition and unplugged injectors one at a time until I found one that made very little difference in idle speed and quality when unplugged. I tried to use a jumper to force it open and got the idle to improve, but it would never clean up. I ended up removing the injectors and sending them for cleaning and flow-matching. The car ran like new again after that, and it only had 22,000 miles when the problem began.

Just another possibility.

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Later,
Vader
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"I'm'a do Things My Way - It's My way or the Highway."

 

I have installed new rapid fires and brass cap and rotor but the problem surfaced before that. It runs like crazy if you get into it but chugs when cruising and when coming to a stop it idles up and down.

 

Mine fluctuates at idle...but only a small problem at cruising speeds. If I have it in drive, and shift it into neutral (at idle), it will jump up to 1450rpm before settling at 950 where it will fluctuate from 1100 down to sometimes 4-600. I was told by a mech. that it was the Idle Air Control. I have cleaned it (lots of crap was there)...and probably should clean it again. But I don't have problems driving the car as far as cruising and accelerating goes.

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Gunmetal 89GTA T-Tops L98
700R4 with 3.27 gears, street tires
Best 60 ft: 1.996
Best 1/8th mile: 9.02 @ 76.5mph with 60' time of 2.14
Mods: air filter, hypertech chip, 3" exhaust
Current Mods: 8.8wires, cap, rotor, +4 plugs, MAF screens
Servo