98 ES 2.5 V6 Idle Surging Code P0122 Low TPS Voltage
 

A little history....

Car had a loose battery terminal and the lights started flickering and the engine ran rough.

Have a Maxscan GS500 so I can read and erase codes.

Fixed the battery terminal issue and the service engine light came on and the idle was surging up and down in a cyclical fashion.

Read the codes...P0122 Low TPS voltage, P0171 system too lean bank one. Also had an O2 sensor code (can't remember the number).

So I purchased a new O2 sensor....changed the upstream sensor near the radiator and that code didn't reset after I cleared all codes, the TPS code was still there and the check engine light reset.

So I changed the TPS.....no change, after code erase, TPS low voltage code came back.

So I tried pulling the battery terminal and putting it back on and then driving the vehicle to relearn the PCM fuel trim.....same code still showing P0122.

Put the old TPS back in.

Looked at my service manuals. Went through the P0122 service check procedure. Checked ohms on the TPS, OK. Checked voltage on connector after removal with key in on position. Voltage OK. Then took PCM out and backprobed connector with Ohm meter to verify connection back to TPS. Both check out. Only one left was to check connector A28 which is a gang connector. Took awhile to get to it in the wire loom under the fuse box. Pulled each of the three connector bars apart and tey wrere all gooped up real good with white dielectric grease....assume they were OK.

Still have the code and surging idle!

Any advise would be helpfull because only other item in the service procedure is to change out the PCM ;)

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One other thing.

Seems the SES light is flickering, not just on.

Wonder if this confirms the PCM is sick ?

Whats the Voltage at the battery ??? I'm wondering if the battery is weak , I'd have te charging system/battery checked to confirn they are proper ... especially the light flickering might be indicating a weak battery/alternator

engine off 12.4V

engine on 14.5V

Both at battery terminals.

So tonight I decided to check again.

Started and cold it had a rough idle...missing somewhat.

Read codes and still had the P0122 with SES on and somewhat flickering.

Erased all codes....threw no new codes.

Idling at 1,800 to 2,000 rpm.

Decided to look at data stream. Noted IAT was at between 102 to 111F, seems high since outdoor temp is around 64F and engine was only running for 10 minutes if that long...maybe problem is intake air sensor?

I think I'll check the IAT tomorrow morning with engine cold to check...

Possible codes not yet set indicate P0174 right bank lean.

Any clues?

So I sprang for a rebuilt PCM on Ebay for $120 w/free shipping....ecuexchange.com

Should get it next week.

Before I decided to purchase this I disconnected the alternator cable and I still had the racing idle problem, but the ses light was on steady and not pulsing.

I'm also going to change out the IAC and also the rear upper O2 sensor near the firewall.

So I hope when I put in the new PCM everything works OK.

We'll see :)

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So Saturday I put in new plug wires, distributo rotor and cap and a new EGR assembly while I had the intake maifold off so I could change the rear O2 sensor. Also put in a new intake manifold gasket and new IAC servo.

The new PCM was also installed.

Started her up and drove about 5 miles to reset the IAC.

3 miles and the SES light comes on.

Also, lights are still pulsing, and the idle is still somewhat unsteady.....

1 Code present...you guessed it P0122 low TPS voltage again!

I ordered a rebuilt alternator................

So my daughter has been driving the car around town, and yesterday the battery light comes on.....thought it was the alternator!

Rebuilt has arrived via UPS so I'll change it on Saturday.

I'll keep you all posted.

Hmmm sounds like I was right with the alternator/charging system check ... might have saved you big $$$

PCM was only $120 including shipping on Ebay.

I needed to change the other parts due to age of car anyway.....

Hopefully this will fix it :)

Still have SES and Pulsating lights
 

Still NG!

Put in a rebuilt alternator from Rockauto.com yesterday, also put in a new battery.

Still have P0122 low TPS voltage and still have pulsating electrical system and SES light.

When I turn on the dome lights they pulse too.

If I turn on headlights and then highbeams, and dome lights then put on rear defroster I get a battery light!

Turn everything off and battery light goes off in about 20 seconds.

I think I'll surrender to the dealer's $4,500 computer, maybe threy can fix it.

And changing the alternator was one Royal PITA!

Took me about 6 hours, and I have a lift!

I've got both service manuals and now this has gotten a little out of hand...checked for another voltage regulator, but it seeems like the PCM does that and that's been changed too.

Totally stumped on this one!

Sounds like a bad regulator ... did you ever get it checked /tested ??? sounds like the regulator is bad , not in the alternator

The PCM modulates the field in the alternator which acts as a voltage regulator....that is what shows in the service manual volume 2 circuit diagram. I changed the PCM also, so there is no other component to replace. There is probably a bad ground somewhere...

I'm saying "take it to autozone advanced ect " they do a free charging system check ...
Your rebuilt unit could be bad ... better then spending hours checking wiring for a part that was bad from the start

Autozone? Why would I want to take it to them?

So I checked for loose grounds....

Turns out the main grounding cable on the driver side of the engine was totally loose!

Had to tighten the 12MM socket head bolt 2 turns just to get it snug.

Restarted the car and it ran perfectly!

Shut it off, hooked up my code scanner, deleted all codes, resterted and took it for a test drive....no more codes and it purs like a tiger!

All repaired :)

Thanks for your help though :)

Everyone should learn from this that checking grounds is an essential part of diagnosing an electrical problem....I learned my lesson :)

omg... yes that makes me want to recheck all of my grounding on my avenger.... i am pretty much following this thread because i am word for word in the exact same boat as you symptom wise... rough idle, flashing lights, occasional can trying to kill itself.

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