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Rough Idle

Hi there. Ive got a 91 Ford Ranger 2.0. It started to run rough about half the time and run fine about half the time. When its running rough, it has a lack of power and the exhaust starts backing up into the cab, so I thought the catylitic converter or muffler was clogged. I removed the catylitic converter and relaced it with a straight pipe and replaced the rest of the exhaust system. The problem seemed solved for a day, then it came back, so I removed the exhaust pipes and started it without, to see if the exhaust system had become clogged and it runs rough even without the exhaust system on it. I dont think its the timimg belt because it will be running fine, then suddenly start running rough, then back again. Also, shutting off the engine for a while seems to get it running back to normal, so it may have to do with the engine warming up as well. I looked at a spark plug and it seemeed fine. Im thinking of doing a compression test next. What do you think?



need to start with the basics rather than obliterating the exhaust system. This could be a vvery simple sensor or control, like idle control valve, air bypass, egr, etc. Any ablility to pull codes on this motor? And looking at 1 spark plug is like washing one hand!. When were the plugs, wires, and other parts that require periodic maintenance done? difficult to try to answer questions when inadequate info is provided. Start simple, don’t throw a bunch of work and parts at it. Fuel filters, fuel line back pressure, leaking air inlets can all affect this. Go about it methodically and get some help from a shop manual which shouldn’t be too hard for this vehicle. EGR systems and dirty throttle body plates get sticky and need cleaning etc…lots of things, mostly minor can cause this.