| Subject: | mitsubishi 3000 gt knocking |
| Question: |
helo anthony my name is jeremy and about 3 months ago i bought a 1991 mitsubishi 3000 gt and when i bought it it ran fine, but today when i started it the idle fluxuaded rapidly. so i just figured it needed to warm up. then i drove it to town, and it kept dying at every stop sign, it was also missing at low to mid rpm. then as i drove it it got worse and worse. a LOUD knocking noise started and it had no power at all, it was not like a valve ticking it was loud. i bearly got it home because it kept stalling, so id start it up and go again just to get home. when i got home i checked the oil which was full then i did a compression check and all cyclnders were around the 150 mark. the motor has about 110k and the previous owner gave me receipts on oil changes and spark plug replacemets so they took care of it i would guess. i also noticed when i was driving today the oil guage was reading lower then normal but not 0. what do you think it coud be? thanks jeremy |
| Answer: | Jeremy, A fluctuating idle usually indicates a faulty Idle Air Cotroller (IAC); sometimes referred to as an Idle Speed Controller (ISC). The ISC sits below your throttle body and it's job is to regulate the amount of air that bypasses your throttle plate when plate is complete closed; i.e. When you're at idle and your foot is not on the gas. When it bounces up and down, that commonly called 'idle surge'. Most decent mechanics will know how to check to the ISC to see if it's faulty. Other causes for this problem can range from a vacuum leak to a bad oxygen sensor. The knocking can be caused by your timing being off. If your timing got thrown off, either due a broken belt or a faulty belt tensioner, it will reduce your ignition timing and cause extremely poor idle and overall power. If the timing belt on this car has not been changed within the past 60k miles (or not at all), there is a good chance the belt is broken. If that is the case, do not risk driving the car again. Have it towed to a mechanic to have it replaced. And for timing belt replacements, I usually recommend the dealership because they have the most knowledge and all the special tools required. But another possibility for your problem is a faulty computer. Read this
article for further information: If your ECU is malfunctioning, it can cause the problems you're experiencing
and would require you to replace your ECU. |