Question about 1995 Geo Prizm
I have a 1995 Geo Prizm LSi with automatic transmission and 198k miles that has recently developed a problem where the engine speed suddenly and briefly decreases. I describe this as a 'stutter'.
It is a very sudden event that results in a dramatic decrease in engine power, but if it happens in isolation the engine immediately recovers. If it happens many times the engine can stall.
The problem happens most often under power at low RPMs, such as when pulling away from a stop. If I place the gear selector in low gear and keep the throttle moderate it will accelerate mostly without issues. I can then shift up into progressively higher gears. As long as the engine RPM stays up it does not stutter as often and it is less likely to stall (probably simply because it can fly-wheel through to the next ignition cycle).
If the AC compressor is on the car cannot accelerate away from a stop without stalling.
During the middle of the day in hot weather the problem is the worst, in cool weather it happens less often.
If it begins to stutter I can back off on the throttle and it will stop. If I don't back off or increase the throttle the problem will usually get worse. I can almost always make it start by trying to accelerate at more than a very gentle rate. If the engine is in neutral it will rev up easily with no stuttering.
The plugs and wires were replaced in within about 25k miles (about 5 years, IIRC). While trying to fix this problem I replaced the spark rotor and cap and cleaned the throttle body. Also discovered that Jiffy Lube removed and did not replace my air filter about 3000 miles ago.
I have removed and inspected the plugs and wires and tightened the valve cover bolts (very loose, which explains the oil all over everything). Also found that one plug was loose, when the engine was running I could feel a slight pulse of gas pressure on the spark plug thingy that seals the top of the plug to the valve cover. These fixes did not affect the behavior of the stuttering issue (or my mileage).
It seems like an ignition issue, but I don't want to just start replacing parts. Are there some procedures I can use to eliminate various parts as the cause of the problem?
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