I am after some advice or know how from you guys please on an issue on my red mx5 before I proceed any further.
Background is I bought the car beginning of June as a non runner which would not start due to an electrical issue which got sorted. It had been unused for 2 years previously. Car is low mileage as according to the car history and dealer receipt of sale when it was imported in 2009 total mileage is just over 49,000 miles.
I got it back up and running but since I have had it the idle is quite low, lumpy and the engine physically shakes on idle clearing as soon as you blip the throttle. The car drives fine and starts hot and cold all OK and tbh of all the 50 odd mx5s I have had seems one of the best NA I have driven performance wise for a stand one pulling really well. To begin with given the nice performance I thought it maybe had some uprated cams which on checking today are standard.
To try and cure the problem I have tried the following but with no success.
1. I replaced the plugs and leads.
2. I fitted a new battery.
3. Did a smoke test to check for any air leaks in the system (all OK).
4. Tried a different known good ECU to see if that made any difference.
5. Tried a different known good Cam angle sensor to see if that made any difference.
6. Checked timing was not out.
Possible other issues..
1. The idle screw would turn but made no difference to revs (it was jammed to begin with needed a mallet to shift it to begin with).
2. Trying to do the idle base reset on the diagnostics tool would not work and idle stayed the same so I wondered if it was working. Checked for power and diagnostics box has 12 (something volts) to it.
3. Engine would idle OK and lumpy shaking idle would stop if slightly higher revs if I unplugged the idle control valve ecu connector.
Finally with a friendly mechanic did a compression test and got results of 210, 210, 210 and 180 (which was a stuggle). Also did a leak down test and mechanic felt it was bad from the exhaust.
My friendly mechanic who did the compression test reckons the low compression on one of the cylinders is causing the car to struggle at idle causing the engine shaking, lumpy nature of idle. My question is before I condemn the engine as needing major surgery is there anything else I should try? I had planned a new fuel filter on the car but see no point based on the compression results.
Thanks in advance.
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