chb88

Hi all
I have a 94 Coupe 6 speed with 90k on the clock. The other day it started idlelng fast when it was hot, 1500 RPM's. I goosed it comming out of a parking lot, in frustration, and the ASR service light came on. I brought it home and let it sit for a couple of rainy days and when I started it it idled fast for a few seconds then returned to a normal idle. However when it reached about 170 degrees the fast idle returned. The ASR light did not come on. I searched the forum threads and all said to look for a vacumn leak, TPS or IAC. Tonight I got a vacumn gage and checked vacumn. Running, its in the 20 to 25 range. When shut off it slowly drops to 0, takes about a minute. I found one of the 3 hose connections to the EGR check valve broken. However weather this is pluged in or not, has no effect on the idle. I did a temporary fix to this with a little RTV Caulk. This will be replaced. When I unplug the IAC nothing changes, still fast idle. However when I unplug the TPS the fans come on and the idle returns to normal. Is this as its should be or do I have a bad TPS? Does anyone know how to test these? I have not pulled the codes for I lost the thread as to which contacts to jump. If anyone knows where the thread is to do this I would appreciate it.
Thanks for the help

chb88

Update
Replaced the EGR Vacuum 2 way check valve, fast idle still there. Tonights test confirmed it only happens when hot, above 190 F. Tomorrow I am replacing the TPS. Anyone have any other suggestions?
I am about to rule out vacuum leak for no matter what vacuum hose I disconnect the problem persist and there are no changes.
WOW nearly 24 hours and no responces... everyone asleep!!!
Help is always appreciated.
Thanks

aminnich

No we are not all asleep. Seems your diagnostics are as good as they get, not much else to say.

chb88

Update 2
replaced the TPS. Now it idles at 1500 RPM all the time, wether the TPS is connected or not, hot or cold. Any one have any suggestions of how to fix this?
Thanks

aminnich

I would check again for vacuum leak, especially under the pass side fuel rail cover. That one fitting with 2 lines coming off of it is especially failure prone. Wish I could be more help, surely other more knowledgeable members will pitch in shortly.

chb88

Thanks but I found this fitting broke and replaced it yesterday. I am very confused as to why I replace the tps and now it idles fast all the time.
Any help appreciated.

aminnich

Ok, I went out and read the FSM for my 95. Prelimanary checks include checking for vacuum leak and PCM grounds being clean tight and properly routed. Next in the list is for a stuck throttle cable and then for throttle body proper operation. Also, with engine off disconnect the vacuum line to the fuel pressure regulator and 'sniff' test it. if gas is present the regulator needs replaced. Beyond that you will need a scan to see if there are any codes. They lumped incorrect idle speed, poor idle, and stalling into the above diagnostics, so some may not be relevant. Hope this helps.

chb88

Thanks again for the reply
I sniff tested the fuel pressure regulator, no gas smell on the regulator but a strong gas smell in the vacuum line. I assume this means the fuel pressure regulator is good.
I am very sure there are no vacuum leaks also
I had a spare IAC, changed that, no difference.I can unplug just about any sensor with the engine running including the MAF sensor without any change in idle speed, currently about 2000RPM with engine hot. I get a check engine light when the MAF is unpluged but it goes out when pluged back in. I am starting to think the ECM is bad. What are the symptoms of a bad ECM?

G-Sting

Have you tried removing the Throttle Body and cleaning it up with TB cleaner? One possibility is that the engine is simply getting too much air, due to the butterfly valves not closing at idle. (I'm assuming your idle set screw on the TB hasn't moved.) Just a thought. Maybe some gunk in there. Won't hurt to clean it up anyway if it's not been done in a while. You'll have to get a new TB gasket, if you remove it. But it's pretty inexpensive. ...just a thought.

chb88

Thanks for the reply
Cleaned the TB about a year ago, 10K miles. Looked inside and it looked clean still. This problem happened all of a sudden, I don't think its an adjustment that is moving. It sounds more like a component failure , something broke or something fell off.

More thoughts

G-Sting

From what I understand, something is causing your engine to get more air. I didn't think the PCM gave it more fuel, unless there was more air going into the intake.

Not to belabor this, 'cause I am learning too, but... Did you happen to open and close the butterfly valve to see if it is fully closing? Is it moving freely--open to close, open to close?

After checking and insuring the throttle butterfly valve is fully closed, see if it remains closed after starting the engine. If it doesn't something is causing it to open.

Since you already removed and replaced the IAC, that doesn't seem likely to be the culprit. (I had a high idle problem a little while back and it turned out that the IAC pintle had a build up on it, causing a rough idle. The previous owner had simply opened the throttle stop a little more to keep the idle smooth, but high. I cleaned the IAC pintle and backed off the stop one turn and wa-la!)

Good luck.

chb88

Thanks again
The butterfly is fully closed and does not move with the engine running.
The fact that I can unplug the IAC, TPS, MAF, And a vacuum thing with wires going to it all at once and nothing happens and the car still runs at fast idle is really concerning and leads me to believe the ECM is not doing anything with the signals being given.
If in fact it is more air causing this if I had a blown Plenum gasket, could that do this?

G-Sting

1. Did you try replacing the PCV valve? (They are inexpensive)

2. Were you able to get the TPS to 'learn' the correct idle position after installing the new one? (Helms: "With Throttle valve in the normal closed idle position, install the TPS on the TB. Align the TPS pickup lever with the tang on the Throttle actuator lever. Then, install the retainers and the 2 TPS screws -- 2.0 Nm or 18 Lb in).

After this, If the ECM/PCM isn't taking inputs from the TPS, it could be the ECM... or it could be that somehow the inputs from the TPS aren't getting to the ECM. ... a short?

3. Finally, the first diagnosis step for a high idle is to use a scan tool to command RPM up to 1500, down to 500, up to 1500 then EXIT. If you are able to accomplish this, you may know the status of your ECM/PCM.

After all this, I am reaching the limit of my experience. Others, please chime in...

chb88

Update
I finally found how to pull the codes on this hybrid 94, OBD 2 connector in a OBD1 system, Jump pins 4 and 12 and read codes on the LCD Display. Way cool, now for the fun stuff, what do these mean.
I get the following:
C12: Diagnostic mode????
H14 Temp signal over 266, I unpluged the temp sensor
H15 Temp signal under -56, Again, I unpluged the temp sensor
H64 Right O2 sensor, I replaced the starter 2 weeks ago O2 sensor is right next to the starter
H65 Right O2 sensor, See above
H66 AC Pressure sensor, I have no clue on this one, the AC works great

Question, can a bad o2 sensor mess up the idle and make it run fast?????
Help is always appreciated
Thanks

aminnich

Not sure, but I would think so. 02 sensor false reading would tell the ecm to put more fuel to the motor, which would in turn cause hi idle.
Again, don't trust my comments alone, wait for replies from those more knowledgeable.

chb88

Update
Rreplaced all 3, O2 sensors. Still fast idle, 1500 to 1700 RPMs. Removed the EGR valve and cleaned it. Nothing changed. Bypassed the vacuum activation valve for the EGR and connected it directly to the Plenum, no change. Manually actuated the EGR valve, Slows a little but still fast and engine runs rough with this. Therfore i assume the EGR is functioning normally.
I cleared the codes in the ECM by removing the battery cable for a few minutes and read the codes before starting. I still have 64, 65, and 66.
I'm about at the end with this and I really need someone to chime in and help.
Thanks

aminnich

I feel bad that this is beyond my scope and surprised others haven't jumped in. Do you think a new post in the scan/tune section might get you some more help?

G-Sting

Definitely try the scan & tune section at this point. Sorry it's beyond me. Good luck.