Larry's Fiero Dilemmas

[The Art Doctor]

OK time I started a thread to fix the issues that are starting to creep up with regular use and bonehead operation.

#1 current high idle issues: seems stuck between 1800 and 2000 which makes driving no fun.

Since pulling the distributor I have been having very high idle issues.  I pulled the intake rubber snorkel tube today to to block off the idle port and check for vacuum leaks.  Well something is up.  Before when I had a high swinging idle issue I covered the small idle port the car would die.  Now it drops way down to 500rpm and keeps running.  I sprayed ether and used propane all over looking for a vacuum leak with the idle port close off and no dice.  Listened all over too and cannot hear a leak.  I next covered the whole throttle body opening and it dies.  The extra air must be getting in around the throttle plate because it is not getting air from anywhere else I can find.   I am not getting throttle to reset properly?  The factory plug over the adjustment screw is in place.

#1a I was not getting a check engine light but tried to see if there were any codes.  Well I was not even getting the 12 code so I tore apart the dash to find no bulb.  Put in the bulb from the seat belt light and get the normal 12 and a 21 for throttle position sensor.  The light does not stay on all the time but the code is there. Could this be part of the idle issue?  It has had a buck and stumble around 3000 rpm just off and picking back up the throttle.  I have a spare from Charlie to try but have been afraid to change as the screws seem stuck.  I only tried removing with a screwdriver like handle tool and I could not budge them. If I use a wrench to get leverage and break them off what is the recourse?  Drill and tap?  lightly nervous about messing this up.

[Fierofool]

While reading your first paragraph describing the problem and steps taken, I was already formulating that it might be the throttle position sensor.  It could be that the stop on the sensor has been bent, holding the throttle slightly more open.  You can bend the tang back slightly. 

Should you snap the screws in the throttle position sensor, I have several intakes with throttle bodies still attached and I know I have at least 1 throttle body alone.  Something you can do before trying to remove the screws is to place a drift or punch against the heads and give them four or five good bumps.  You could also spray them with a shot of keyboard cleaner.  Turn the can upside down so it sprays liquid.  Do this 3 or 4 times letting them defrost before the next shot, bump them with the drift and then try to loosen them.  That should shrink the screws and the bump should free them.  Of course, put some never seize on them when reinstalling. 

An impact screwdriver is also very useful in this situation.  https://www.harborfreight.com/search?q=manual%20impact%20screwdriver

[GTRS Fiero]

Another potential issue is carbon deposits.  Deposits build up around the IAC hole, but can also block the throttle plate.  I wonder what would happen, if you blocked off the IAC tube, rather than the IAC hole.

[scottb]

Cracked EGR tube....... may have been bumped pulling distributor

[GTRS Fiero]

Somehow, I thought that had already been checked.

[The Art Doctor]

The wife told me to put on my big boy pants and just get out there and turn the screws and if they break just deal with it.  Ill try the tricks above and hope for the best, tomorrow, when its not dark, hey is that a cat over there.....


The EGR tube is a Fiero Store braded hose type, not so easy to crack as a stock type. https://www.fierostore.com/Product/Detail.aspx?s=67019
 Yes, it could still be the culprit but I did give it a heavy dose of combustible gas and it had no effect on idle RPM.  Can it be removed and blocked off without having to disassemble anything else?  Enough room to turn the two bolts out without having to mess with the manifold itself?

[Fierofool]

Yes, some have done it, but it's a tight space to work underneath the manifold.  You would need blocking plates for both ends.  There are also some reports of burning pistons when the EGR system is deleted. 

Try bending the stop tang on the TPS before delving into the alternatives. 

[Fierofool]

Has the intake ever been removed?  Did Alan remove it when the plug blew out?  Or has the EGR tube ever been removed?  Has the throttle body ever been removed? 

[GTRS Fiero]

The intake end is very tight.  I think you could block just the intake end, temporarily.

[The Art Doctor]

I know the intake was removed to replace injectors just before I got it. No idea if the TB has been messed with, but the bolts don't look boogered  up.

I don't recall bumping the TPS arm but it certainly is part of some issue as its throwing the code. 

[Fierofool]

Code 21 indicates a high voltage.  Does anyone know if the voltage increases as the throttle is opened?  If it does, that may be a good sign the stop tang position has changed. 

Voltage to the tps should be 5 volts.  You can test the voltage feed by probing the feed wire with positive lead on a meter and grounding the negative lead to the frame, not the engine.  Ignition should be in the ON position. 

I found this on testing for high voltage on a TPS.

I’m not sure why you are getting such a high voltage, but you are making one mistake when checking TPS voltage. The ECM sends a 5 volt reference voltage to the TPS which passes through a variable resistor of the sensing circuit. This of course is connected to your throttle pedal. When the 5 volts passes through the resistor of the TPS, the voltage will vary based on the position of the throttle plate. This is how the ECM knows what you are doing with the gas pedal.

You can test a TPS in two ways, You can simply test the resistance with an Ohm meter or you can test the voltage change that occurs in the reference circuit. The mistake you are making is connecting the multimeter to the negative battery post. You need to connect one end to the 5 volt reference sent to the TPS from the ECM and the other lead to the center wire coming out out of the TPS. This is what they mean by inline. While doing this, with the key on, move the throttle plate and the voltage should change smoothly. It is the smooth change in voltage or resistance we are looking for. If it glitches, jumps or just doesn’t change, you need a new TPS.

To add, a TPS won’t make a car not start. You need to check the fuel pressure, check for spark and injector pulse.

[The Art Doctor]

TPS was it.  Yippie it worked.  I use an impact driver to loosen both and was successful on getting the top bolt out whole.  The bottom one loosened and made around two full turns before the bit finally stripped out the rusted female t25 end.  With it now loose I could slowly grab the head swing the TPS around and with vicegrips slowly worked it the rest of the way out resetting each 1/4 turn.  These must have been factory bolts as they had blue thread locker on them and the TPS had the factory paper label.

Idle when right down, actually better than before.  Fairly stable between 950 and 1025.  I guess it was fully unrelated to the distributor but funny that it decided to let go at just that moment.  I have only taken if for a short ride but it was running super. 

I switched the ICM back to the new one this morning to see if it would help with the stumble which came back with the old unit.  This was prior to the TPS switch out.  I didn't notice a stumble this morning but it is irregular.  Drive time will tell.

Now the code is still there, I checked.  Is it worth it to resent the ECU again or just leave it be as its working?

[Fierofool]

Disconnect the ecm power near the battery anytime you replace a sensor thats read by the ecm.  That way if it comes back you'll know for sure that you have an issue.

[GTRS Fiero]

Glad it's getting sorted.

[The Art Doctor]

Next issue.  The factory installed belt squeal remedy.  Should I go with the Rodney Dickman fixed idler pulley and longer belt or Dodgerunner's spring active belt tensioner?  Rodney's looks easier to install so I'm leaning that way.  Any opinions?