M50 Throttle Stuck / Engine surge

[e30pdx]

Happened twice yesterday and once last week. Engine suddenly spikes to 4000+RPM’s. First time I was in 1st gear so I braked, clutched and blipped the throttle and it stopped. The last time, I had to kill the engine on a busy street because it just kept revving. Any common / relatively easy things I can do to diagnose?

Throttle cable appears to move freely, though I worry about the plastic housing where it terminates being the culprit (there is some hose running just above it). IAC? TPS? MAF? Other? I’ll lube the throttle cable for good measure, but engine only has <10k on top end rebuild and transplant so I was hesitant to start ripping into the Throttle body and/or IAC. At idle and under all other circumstances the car otherwise runs smooth and clean.

Thanks!

Haven’t done a smoke test yet.

[e30austin]

Start by cleaning the ICV. Check for vacuum leaks at both ICV hoses and the connector that fits into the back side of the intake manifold.