another weird idle problem

[MRX]

this outta boggle some minds. Ok first my speedometer is cutting in and out...i'm come back to why i mentioned that. Whats happening is that after i let the car warm up then drive about 5 or so minutes down the road through stop and go traffic i get a CEL and anytime i'm not giving it gas the revs drop fast and past the idle point. Forinstance i'm coasting at partial throttle going 30 mph and i'm coming up to a traffic light. I press in the clutch, let off the gas and i'll get a CEL, or i'm slowing down clutch in and press the brake...get a CEL, even when i'm doing say 50 i let off the gas and get a CEL. After the CEL comes on and i'm at a complete stop the idles at like 100 rpm, raises like 4-500 rpm but then settles down somewhere in between if it doesn't cut off. If i turn the car off and restart it sometimes goes back to normal idle if it doesn't cut off again. After restart the CEL comes back if i let off the throttle. I'm pretty sure it has something to do with the throttle plate when its closed but heres the weird thing. If the speedometer is working...the car is perfectly fine. I can let off the gas as quick as i want and it catches the idle point everytime but as soon as the speedo stops working and i let off the throttle...CEL. I have the a6 intake manifold from a junkyard and i'm not sure how long it had been sitting there but could there be a problem with like the icv, iac, fast idle thermo valve and such? I still have my other intake mani so i have idle parts to try out but what in the world does this have to do with my speedo???

[91accord4door]

so what code is it throwing?

[MRX]

haven't even gotten the chance to check yet. Everytime i go to the shop they're always busy. I know i need to check but i'm just seeing if somebody has gone through this b4

[91accord4door]

sounds very strange,you should check the code yourself.you know how to do it right,that will help us figure this out.