I think I know why my car have poor preformance. I think this time is for sure.

In order for my car to work a little better i had to move my TPS totaly off factory spec. the factory spect for the tps is 0.5 at idle up to 5.4 volt at WOT

my tps now read as follow. at idle 9.20 up to WOT 6.53

so you can see when I open the throttle the tps is sending very wrong information to the ecm. basicaly is sending information the other way arown

but if I ajust the tps to spec. the car will have bad idle and the engine stop. making it imposible to drive. so the idle is very bad. to the pont that even the tps is off i have to move the distributor some degrease counter clock wise

so in order to the war to run my tps is off and my distributor is off.


the tps and distributor is compesating for another problem. other member toll me that some time ago. but did not know what was causing the problem.

now I think the problem is the IAC valve. I will have to do some test, but Iam preatty sure that is the problem.

I will report baack after testing the IAC

 

The tps receives 5 volts from the ecm. If yours is over that, your ecm may be wack along with your tps and maybe your voltmeter.

 

very interesting. them my computer is wack. but if i set the tps to the right position I will get spec reading

 

TPS should show ABOUT .5v when set correctly at idle, and ABOUT 4.5-5v at WOT.

You're no where near that, and your volts are moving in the wrong direction. Are you SURE that your equipment and methods are correct?

 

If you set it where it should be, and it runs like crap, then the computer isnt responding correctly to the voltage. h

 

OR...there is another problem.

 

.............Well thats a helpful answer. h

 

Hi Hitmanpty
Here you go this should help you, although my shop manual is for an 85 and the 86 had a different ecm. You should still have the same voltages and fault finding, but there are probably differences in the ecm plug numbers/locations. The tests should help you track down the problem you are experiencing.

Hopefully someone with an 86 shop manual or agent86 may let you know the ECM connections for the 86









from the corvette brothers down under

 

Hi

As the tps increases the voltage (like a variable resistor) if the wiring is not right you could be decreasing the voltage via the TPS.

I would start confirming the wires go to the correct position in the TPS connector plug, you should be able to do this from one going to ground via ecm and the other having the 5 volts.

If the wiring are in the correct locations you may have a short, i know the injectors are supplied 12 volts. The ecm grounds them in pulse widths, so maybe you are picking up the 12 volts from injector wiring? You may have to start stripping back the insulation to check and see.

No need to think the IAC is bad unless the ecm has the correct readings for the TPS, fix that first then you can do the base idle again and set the IAC position. (the base idle setup when you short the diagnostic terminal ignition on and remove iac connector will put everything where it should be for the ecm to operate things correctly)

The 416 wire color for TPS is GREY, 417 DARK BLUE and 452 BLACK. that should help

Good luck there

 

ok today I move the tps to spec. Iam getting 0.45 on idle and 4.6 at wot.

I install a new IAC. (why not here in panama is only $22.00 and the old one is 27 years old) I reset the ecm.

them when I was going to start the car. no battery. so i take the battery to the shop for slow charging. i will get it back tomorrow and we will see if the car improve

what i like to do now is check the old IAC now that i have it in my hand, but dont know how.

 

Hope you mean 0.54. h

 

yeso 0,54 Sorry

 

ok I test the car . I dont know what the problem is.

hart to start on cool. car no idle on drive or reverse. good idle on parking. imposible to drive

I will start a new post with details on what I found.

 

Ok now you have to do the base idle again ( you need to every time a major change is made or something was out of spec)

when hot.

Connect a paper clip, to your diagnostic terminal under your dash connect to terminal A and B (the top right two pins).
Turn on ignition but don't run the engine.
wait at least 30 seconds and then remove the idle air valve connector (IAC) (the square plug) then turn of ignition and unplug the paperclip.
Now remove the timing connector a single wire near the fuel pump relay.
Start your vette and set the idle speed to 400 rpm in neutral (auto trans) 450 rpm (manual trans) then check your throttle position sensor,
the top two wires it should be set to 0.54volts dc, also confirm with engine off that the tps rises to 4.5 volts at full throttle.
Turn of the ignition and reconnect the iac valve connector and timing connecter and start your vette.
it should go to 1200 rpm then drop slowly to 600 rpm, take the car for a 15 minute drive with the usual stop lights.
It is normal for a little hunting while the ecm relearns, also do a few spirited take offs.
All should settle after 15 to 30 mins normal driving and have a stable idle.
..

Good luck hopefully now your car will start easy cold and idle correctly.

 

ok i do that first thing tomorrow se What happend

 

Ok just preform the test
at first the engine was cool. (have in mine I live in the tropics. no snow here) so it took me some time to get it started. like 10 times and some time more playing with the gas so the car dont stop.

once I get to the normal temperature I can stop playing with the gas pedal the car idle ok in parking gear. . I turn of the car. and do the hole paper clip process

after disconecting the IAC I try to put it in Drive gear. impossible task since the car stop running . stall them stop running. same goes for reverse gear.

so I stay some time in parking. turn off the engine. reconnect the IAC. I had to forget about puting the car in drive gear. Like I say that was imposible.

after reconect the IAC. no change. the car idle on parking but the moment I shift to drive or revers the car stall and stop.

I even have some intake back fire trying to keep the engine running.

so.
TPS at spec
new IAC
did the paper clip reset procedure.

I see no change on the preformance of the car. did not get a change to tested in the street. since it will not work on drive gear

please advice

 

Hi that sounds like the ignition is too far retarded to me.
With the base idle procedure the IAC valve gets put in a position to have around 400rpm in drive, if your tips shows 0.54volts dc then it should idle. Double check you have 6 deg before top dead centre the std timing for the TPI
Then adjust your idle screw to get 400 rpm in drive. Then readjust TPS to 0.54volts dc and re- connect everything.

If it still does not idle and you have at least thirty psi fuel pressure the next thing to look for will be a vacuum leak at the runners.

You are almost there so don't give up !
The ECM cannot run the engine unless TPS and distributor timing and base idle throttle body adjustment is all correct. If one is wrong it will go e what you are experiencing hard starting cold or hot.
The TPI should run smoothly at 400 rpm in drive
Good luck
Sorry have been on the road driving interstate for work 700 km will get a message usually on my smart phone within half hour of it being posted so let me know how you go
Cheers
Gerard

 

I have a timing light. I will run my engine into hot, and then will try the timing light. and I will ajust to 6*btdc.

then I will check the tps for 0.54 volts on idle.

I will come back here to report findings

 

Ok

just remember while setting the base idle the ECM has no control while this is being done, if you are still having issues at trying to get it to idle at 400rpm and have correct TPS volts and Timing. CHECK your EGR valve exhaust gas recirculation valve is not sticking or stuck open, that will make it impossible to get it to idle. It should not be open even with normal idle it only operates in pulse widths during steady highway driving.

Once you get the base idle setup only then can the ecm manage your engine correctly, for cold or hot starts to be easy and quick.
It is very important to double check everything is up to spec, including making sure the IAC valve was disconnected after at least 30 secs with ignition on while the ALCL terminals were jumped.

Then turn of ignition and remove the jumper and start the car and set to get 400 rpm in drive.

Good luck

 

i Have no egr valve . i delite that some time ago

so to set the base idle, the ecm most be disconnected. just the get it out of the ecuation right??????