Hi, I have a 1991 s10 Blazer with a 4.3l v-6 engine. The truck has a ton of miles on it 135,000. But, I've owned it since it had about 80,000 miles on it and I've always done whatever maintanence on it that was required. Up until recently my truck has run great with no real problems. But, a few months ago I noticed that the engine started randomly mis-firing whenever I was stopped in traffic. This mis-fire went away as soon as I began to accelerate. I figured it was just time for a good tune up. So, I replaced the spark plugs, plug wires, cap & rotor, pcv valve, air and fuel filters. I also cleaned off the throttle plates and IAC valve and passage with spray cleaner. I was surprised that the engine still randomly mis-fires when the truck is in gear and at idle. Increasing the engine speed just a little bit seems to clear up the miss.
Also, there are no check engine codes present.
I'm thinking with 130k miles on the engine the mis-fire could be coming from a intermittently leaking engine valve or two. I guess a compression test is the next thing I'm going to have to do. But, I'm not sure if a small or random leak would even show up. I could use some help with this mis-fire.
Random misfires are weird there could be so many things causing it, this calls for back to basics testing unless there are codes, vacuum leaks, fuel pressure and fuel bleed off, if it misfires the ecm will hit the mil soon I cant believe its not on now, let us know we will try and get you fixed, oh have you had to add coolant since this problem? Nd how did the plugs look
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