MK1 Idle/Throttle Issue

EdHeighton · 2025-10-06T04:57:26-0400

Hi. I have a MK1 MX5. We had a turbo one come into my work a few years ago so I brought the engine complete with the kit and dropped my original engine and installed this one with my brother in law. We did this over a weekend and it seemed fine, but had a leak on the exhaust manifold. Then life got in the way and we never got to finish it.

Earlier this year we started again and sorted my poor fitment of the manifold but still there was a leak and now we have noticed the idle is poor and the car cuts out over 2k revs. I just need some guidance on what to check as this wasnt an issue before.

He is busy now with his family so I dont want to bother him and I want to learn myself, but dont know where to start. Any help is appreciated

Martin Y · 2025-10-06T12:24:06-0400

Hi. I think I saw you post this issue before, maybe on FB.

Anyway, my first thought of a car that won't rev over 2,000 is that the ECU thinks the engine is idling, so it cuts the fuel if it thinks it's running too fast.

On the early 1.6 with manual transmission, the throttle sensor is a simple switch which indicates throttle closed or throttle wide open. If it was getting a false throttle closed indication, it might assume the car was just idling all the time. So I'd look at that connection on the throttle.

There are 3 wires: Light green/White, Black/Light green and plain Red. The Black/Light green wire is a ground, and should connect to one of the others when the throttle is shut (the Red I think but I'm not 100%) and to the other one when it's wide open. So, if a wire has got pinched perhaps, and that red wire is always shorted to ground, that might cause the symptom you see.

EdHeighton · 2025-10-06T13:38:07-0400

Hi! Yes I did but I can't find my post to re-read the replies and lifes just got in the way for a few months! I'll try get out at some point this week and check this! Thanks for the response

MK1 Idle/Throttle Issue

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