no start/no idle -95 atx

[SHOinNC]

Pulled codes on a friends snap on scanner and all I got was 124.Tps is new, intake gaskets are new, just replaced the TB gasket and EGR gasket tonight ,fuel pump is almost new 155lph,IAC valve is new,60k done in the spring,CPS,CrnkPS,EGR DPFS is new.Only sensor I can think that hasent been replaced is the ACT and MAF sensor.Problem is she wont start.If I hold the throttle slightly open it will run,and will idle when warmed up.It also surges at highway speeds. Friend also did a smoke test in the vacuum lines to check for leaks, none found.When the car does warm up and idle it is very erratic,anywhere from 500 up to 1500 rpm. Thanks for any suggestions, Richard
95 ATX

 

[projectSHO89]

Your starting and idling problem sounds to be related to the IAC.

I see that you have a new one installed, so, assuming it is good, there are several additional items to check.

First, make sure it is plugged in! Then, inspect the "nostrils" in the intake to make sure they are not clogged. They are the upper pair of holes visible through the open throttle plate, the lower pair of holes is for the EGR. There is also a passagway through the throttle body itself for the IAC inlet air. Check it also.

For the 124 code, pull the TPS and make sure the center shaft connection is properly positioned on the plate shaft with a closed throttle plate. Some sensors can be installed out of phase.

If all of those check out, it will be time to get out a meter.

For the TPS, backprobe the center wire of the connector with the KOEO. It should measure just under 1.0 V (.6 to .95 V is typical). Monitor the voltage while opening the throttle by hand, the voltage should smoothly increase to around 4.5-5.0 V.

For the IAC, backprobe the RED wire with KOEO. It should read battery voltage. The other wire should have a variable voltage on it, depending on what the PCM is trying to tell it to do. If it reads the same as the RED wire while trying to start the engine, then there is either an open circuit in the wiring to the PCM or the output driver in the PCM for that solenoid has failed.

Hope this gives you a few things to check.

Steve

PS If you don't have one, Sears is currently selling a basic digitial meter (34-82082) on sale for only $9.99. If you wait until Saturday morning, you can save an additional 10%.

 

[Anthony1238]

This just happen to me last week... Did you check yout Iab Valve...

This was the Problem with mine..did you replace the gasket, Check the electricial side of the part...the problem on my car was a fault on the switch side of the valve, the mechanical side works fine...

 

[SHOinNC]

Thanks for the replies. I checked the tps voltage with the scan tool about .84 on the low end and 4.9 or so at wot. I changed the IAC valve about a month ago.with new gaskets .I know it works, the idle goes up and down.With the air box lid loose you can hear the valve open when the engines idling, barely.A slight hiss and increase in rpm. I think the SHO gremlins have reared their heads once again!! Richard

 

[SHOinNC]

Hey Steve ,I checked the tps voltage. its good,but the iab voltage is 12 to 13 volts on both lines all the time(12v engine off/13v engine run)..I guess this operates similar to a fuel injector, having 12v and using the ecm to control the ground.Is this correct.Do I have a ground problem? Thanks, Richard

 

[projectSHO89]

Richard,

Yes, that is how it operates. The PCM applies the ground tot he low side of the coil as a variable duty cycle squarewave. The electromagnetic force will be proportional to duty cycle. As the actuator is pushing against a spring, it is possible for the PCM to precisely control the amount of opening of the valve. The PCM measures the IAB's effect on engine speed by monitoring the crankshaft speed via the CPS.

If you measure battery voltage on both wires of the IAB with the engine running, then the problem is either

1) Open circuit between the PCM connector and the IAB connector. Measure between PCM connector pin 21 and the IAB connector O/BK wire. Be sure to wiggle the harness to see if the connection is intermittent. It is possible that the wire has broken inside the insulation.

or

2) Defective PCM (either the output driver has failed or the driver has not been turned on due to some other internal fault).

 

[SHOinNC]

Steve, I belive I found the prob. If I lift up on the harness that runs through the engine valley the idle picks up like normal.Looks like I'll be pulling the intake again to find and fix the wire. The short must be close to were the iab wires go into the main harness under the tb. Thanks for all the info. Richard

 

[AutoSHO]

There is a ground in the middle of the valley for that wiring harness, make sure you check that!

Also check the ECT wiring, its related to engine idle strategy as well. Sounds like you found the problem!

 

[projectSHO89]

The problem is not a "short".

The problem is an "open".

Look for a broken conductor inside the wiring insulation.

Steve

 

[SHOinNC]

Thanks to y'all for the great info.Havent gotten around to fixing it just yet.May start pulling the intake tonight.If y'all have any blend door actuator probs and need parts, shoot me a message and I'll try to help.I can get the internal parts
Richard