C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

trouble with my 85

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Old Sep 13, 2009 | 08:00 PM
  #1  
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miketo
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Default trouble with my 85

I just bought a stocked 85" drove great till it started misbehavin.have code 32 egr & no vacuum to egr solenoid input. car runs good cold and lopes when warmed up. traced vacuum that splits and connects under throttle body then connects to front eecs canister,both have no vacuum
the eecs solenoid has input vacuum but no output vacuum to eecs canister
does this feed both throttle and egr solenoid and causing the problem?

i checked fuel injectors and they all read 16.5 ohms, I have read most of the threads on similar problems and tried most suggestions
when I start it warm, it will start for a sec then shut off, if I take off the air intake, the car starts and stays on
with foul smell and idles eradictly after a while
. any suggestions? hate to see it parked !!!!!

Last edited by miketo; Sep 14, 2009 at 06:43 PM.
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Old Oct 15, 2009 | 07:34 AM
  #2  
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The EGR isn't, or shouldn't be, keeping it from starting or running. No vacuum to the EGR valve means it's closed, or should be. The EGR code is telling you that the valve is Open (and that the base of the valve is hot and staying hot for longer than the ECM thinks it should). The code also could be setting because the Switch it uses is bad - this is actually the usual cause for that code happening, a bad switch, nothing wrong with the EGR valve itself

Do this: unhook (and plug) the vacuum line at the EGR valve itself. Start the thing up and use a screwdriver or small pry bar up underneath the valve to Lift it (you can also do it with a hand vacuum pump hooked to the valve, it's a Pain to get up under the valve in the TPI manifold, but it can be done). At Idle you will be able to tell instantly the difference between valve open and closed, and it Should close under it's internal spring tension. As long as it's Closed it's not bothering anything and the car should start and run normally. There will be an effect on Emissions if the EGR isn't hooked up, but at least you will have found your problem.

There is also the possibility that the valve is Closed, or trying to, and that the port or pintle are fouled with carbon and preventing a good seal. Result - vacuum leak and bad idle.

If the EGR valve isn't Closing then it amounts to a big vacuum leak, which will really mess with the idle, if it'll idle at all. There Should be manifold vacuum at all times at the small port on the bottom of the throttle body, if there isn't then you have something wrong, which Could point to a major vacuum leak somewhere else. Could also be that the port is plugged up - have you removed/inspected/cleaned the TB lately?

By removing the MAF sensor (either by taking it off the TB, or just unplugging it in place) you force a Zero air flow reading and thereby force the ECM into a mode where it ignores that air flow reading and uses a set "lookup" table instead. This is a default or "limp-in" mode, and normally if it'll run, even if poorly, from that table and Won't run from the MAF then the MAF is faulty. Normally. A major vacuum leak will mess with the MAF to the point that it's reading, particularly at idle, is so far below what it Should be that the diagnostics will think the MAF has failed.

Keep in mind that the '85 uses a one-piece control module to power the MAF, not the two relay setup on all other years. I have NEVER seen one of those MAF modules go bad. Never. Not saying it can't happen, but it's about the Last thing I'd be worried about. It's an expensive part to Buy, also..
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Old Oct 17, 2009 | 08:33 PM
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miketo
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thanks for the info, I will do all that was suggested as soon as it stops raining
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Old Oct 22, 2009 | 07:24 PM
  #4  
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miketo
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ok, so I took the tb apart and found much carbon build up ( snapped one of the torx screws but I was able to remove it). the idle air control valve sensor was black so it was ordered (it will take a few days) is this what is causing the problem? the port under the
tb connecting to the egr solenoid did not seem to have any blockage. the repair manual
indicates that the valve on the idle air control valve should only extend 1" 1/8, I checked it to extend 1" 1/4.
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