very high idle

[Johnty h]

ive just replaced my engine on 172, all back together now and I go to start it and it just revs really high but like someone was pumping the accelerator, so I turned it off checked for loose pipes etc everything seems to be fine? so i cleaned the throttle body with carb cleaner go back to try it and the red light is on and no fuel pump? i keep turning on and off a few times and it fires again still the same. then have another look and red lights on again its intermittently coming on and off? all the auxiliaries are off my original engine and in perfect working order or was. Also the starter motor wire is really close to the manifold and i cant seem to get the heat shield back on? does this need to be on before the manifold? any help appreciated

thanks

john

 

[JON FOZ]

Sounds like a big air leak behind the TB

 

[Johnty h]

the throttle body itself is buzzing like mad when I take the induction pipe off its like its trying to open and close itself and you cant open the valve until you disconnect it? is it a new tb time ? cheers

 

[Ol’ Tarby]

Not trapped a HT lead under the inlet manifold have ya?

 

[Johnty h]

ive just taken that off to check the plugs I don't think so and tbh it was revving a lot less after I gave them a good clean. something to do with this buzzing im thinking.

 

[Ol’ Tarby]

The throttle body does buzz when the ignition is on

 

[Andycarr172]

Sounds like throttle body failure to me. If you start it with the electrical connector disconnected it should idle at around 2000 with no throttle response so check the connector first

 

[sanerr]

I've heard that the throttle potentiometer that's connected to the accelerator pedal can cause problems when a motor is swapped. You're best to try get the one out of the car the motor came from.. Or try track down one from the same year and try that?

 

[Johnty h]

Sorted guys! Was a dodgy earth strap thanks for all your help

 

[Shellcase]

@Johnty h
Which one was it?