I found a guy who is really good at tracing problems. After replacing about every sensor and cleaning tb resetting the idle.checked the mass air flow sensor and burn modual,both are working fine.we found an orange wire near battery.(85 vette) by the way when you start the car the check engine light comes on and car runs lousy ,step on the gas and it runs like crap,so bad you can t drive it.when you disconnect the orange wire and reconnect it while its running the light goes out and the car runs 100 % shut it off and restart it an back to lousy. I put a switch temperarily on that orange wire in order to drive the car.the next thing he suggested is to checkthe wiring from the ignition switch.does anybody know where i can get schematics for the switch.or have any other ideas .thanks again

 

If the MAF power and burn off relays are original (or even 10+ years old) I'd replace them both (less than $40.00 for both). They are located near the battery on my '86. I was getting an intermittent code 34 and the relay replacements solved it. If you need part numbers I can look it up tonight.

Steve

 

totally discusted,any ideas would be appreciated,another mass air flow sensor was installed,had about 10 starts without light coming on,then started again,light only comes on at start up.thanks

 

Do you have the Factory Service Manual? The diagnostic chart for code 34 is pretty short (in my '87 FSM, at least). My scanner is on the fritz so I can't post a copy, and you should really use the chart for your model year.

I do not have experience with this fault, so the following comments are based only on what I see in my FSM:

The orange wire provides battery voltage to the MAF burn-off relay, MAF sensor via the MAF power relay, and the ECM. The switch you added could be affecting any or all of these, depending on where in the circuit you put it. The connection to the ECM is interesting as a faulty ECM is one of the possible outcomes of the diagnostic chart.

If you start the car with the MAF sensor disconnected does the idle improve? My FSM says this indicates a bad MAF sensor (which you've already replaced). If it doesn't improve then a dirty or misadjusted throttle body may be the culpret.

If you disconnect the MAF Sensor and start the car does a code 33 set?

If yes then the MAF sensor is bad.

If no then circuit 998 (dark green wire) may be shorted to ground or the ECM is faulty.

Good luck & get yourself a FSM right away if you don't have one already.

 

thanks for the help ,i really appreciate it.i reconneted that orange wire,and then tried to clear the 34 code by disconneting the battery,could not get it to clear,is there something else you have to do to clear it?i have a brand new mas sensor to try.i do have a fsm but got away from it lately.the 85 is totally different from the 86 or 87because of the burnoff.next i m going to try the green wire if i can find it ,thanks again.

 

No, its not different actually.
87 has power and burn-off relays. I suspect your orange wire goes to one of the 2.

Might be a replacement wire for one of the fusable links that someone failed to diagnose properly. Might be the left overs from somebodys fan switch since the relay is nearby. There is a lot going on in that area. Finding where a wire goes and what it leads to is not that difficult.

The power relay has 5 wires, burn off has 4. Or vice versa...

The relays are the same. Trade them around. Unplug the MAF. That forces the system to run open loop and aids in diagnosing.

Take the battery out, and the tray it lives on, and physially trace all the power source wires that go to the jumper post behind the battery AND their fusable links hidden under the battery tray. Your orange wire MAY be the source wire for the jump post....if so, thats where the ECM and all the control features get their power, not from the FUSE panel. The circuit might end up going thru the fuse panel but the source is the jump post thats got fusable links between the post and the system that it serves.

Trace the relays wire back into the harness.

Next, follow that harness section (branch) to the trunk-line on the firewall and look for ANY sign of cracked or broken insulation. The harness is fragile at best. There are LOTS of splices in that area and multiple grounds that absoluetly must be clean and tight. Not battery grounds, harness grounds. The FSM will tell you where they are. The most important one is near the oil filter and has all the control system grounds on one bolt on the block by the filter.

 

I think I read somewhere that the '85s have a MAF burnoff module inside the dash.

Some MAFs put out a varying frequency instead of a DC voltage. Do the '85s have that kind of MAF?

 

The 85 vette does have a burn of module, the mass airflow sensor on the 85 is analog you can fit the later digital one... i am running a 89 maf without issue.
If you own an 85 you really need to look out for a spare burn of module only the 85 came with them so get one when you can nice and cheap.

Remember always disconnect your battery to reset any stored faults as i have found from previous experience, the ecm will try to compensate. The vette will run badly till the power has been disconnected.