My '83 GTV6 when fully warmed up has an odd idle and wonder if anyone has any ideas?
The revs slowly build up by 300 to 500 rpm over about 5 seconds, then suddenly drop back to 900rpm. Then does it again in the same 5 second rhythm continuously. Embarrassing sitting at the traffic lights.
Idles rough as when stone cold (AAV restored and seems fine).
Idles fine when warmed up midway to around 40 C/100 F.
I've replaced all the engine hoses except the intake couplers, which seem o.k. as far as I can see without removing the plenum. Shoo-goo all the cracks on the ribbed intake tube. Have done all the grounds in the engine compartment. Cleaned all the ignition related connectors, including the ign. module.
Timing spot on (1983 doesn't have vacuum advance).
Rotor & distributor cap cleaned.
Spark Plugs look good.
AFM has been fiddled with, as there is white sealant on the plastic cover.
Might run a bit rich as it seems to splutter when I slow down to low revs whilst driving.
It's a bit smoky, not visible, but can smell it. Speedo reads 81,000 km, so reckon it's probably 281,000km.
I plan to check fuel pressure next (for pump and pressure regultor), but that may vary with the revs anyway. The fuel filter looks shiny on the outside, so I assume it's new. Perhaps should replace that and the air filter anyway.
Cold start injector fires o.k., but haven’t checked it for leaks.
The slow rhythm (5 second) makes me think it's not ignition. Vacuum leak I would've thought wouldn't have an effect only when hot.
Turning on the air con smooths it out (but feathering the throttle doesn't), so maybe the throttle coming off idle position and the throttle idle switch being tripped?
Any suggestions anyone?
1983 GTV6 Funny idle
Al Campbell