dms0309

What is the purpose of the MCS on an 85, how does it work?

Tom400CFI

I don't think that there is any such thing. Early 80's Carb'ed engines had an MCS in the electronically controlled Carb...but not an '85 'Vette.

Where is this item located on the engine?

dms0309

I had a mechanic check out my car, said it has something to do with emissions and said I should replace it. Could he have meant something else.

Tom400CFI

Warning...Will Robinson!

I'd ask the mechanic from more details. Something is amiss w/either his diagnosis or your interpretation thereof.

dms0309

Thanks guys, I think I'll have to talk to the mechanic about this. Sounds like there is a (I hope) a misunderstanding some where.

Cliff Harris

He's probably talking about the IAC - Idle Air Control. Typically the passages in the throttle body get dirty and cleaning them will fix IAC problems in most cases (and not require a new IAC).

It's possible he's talking about the TPS (Throttle Position Sensor). They do need to be adjusted. They seldom fail.

Another possibility is that it's the EGR (Exhaust Gas Recirculation) valve. The EGR passages can get plugged up with carbon. There's also an EGR solenoid involved that controls it.

tunedport85inject

Charcoal purge cannister solenoid,EGR solenoid,air pump diverter valve solenoid... lots of solenoids involved in emission stuff...

Tom400CFI

Yep. COULD be one of many things....just a bunch of WAG's until we hear back from the OP.

dms0309

I asked him to check the car because it has a hesitation on acceleration from dead stop, he meant the EGR solenoid. Said I could change it myself. Is it an easy job. Thanks

Cliff Harris

My experience is that a hesitation off idle is caused by a vacuum leak.

I guess an EGR valve stuck open would qualify as a vacuum leak. In my case the EGR solenoid was bad and caused the EGR valve to stick, so both of these need to be checked.