: Code P070 with stalling and surging-TPS or ISC?

04-01-12, 10:48 PM

I've been reading this forum like crazy for a week and now have enough info to post my question.

This was my dad's 1995 Concours, Northstar, 65,000 miles, otherwise in excellent condition. I inherited it upon his passing last year and I want to keep it.

The car has 4 symptoms:

1. Low-speed stalling, about 20-35 MPH. I can get it to happen more often going up a hill about 30MPH, quickly release the gas pedal (to create a fast decrease in RPMs), and it will stall. It also happens during low-speed 10-25MPH turns, starts right up every time.

2. Slight low speed "miss". Almost like in the older mechanical fuel pump days when a defective fuel pump would give you a high-speed "miss", except this is at low speed, 20-35 MPH, especially with the cruise on. Noticeable, but not overwhelming.

3. The idle seems to vary in Park. There's no tach on this car but if I had to guess it varies about +/- 25RPMs, probably around 650RPM. Again, noticeable but not overwhelming.

4. Driving 20-35 MPH, release my foot from the gas pedal, and about 1 second later I get a surge for a split second, almost as if I tapped the gas pedal.

From reading these forums I removed the EGR valve (pryed that awful fuel rail out of the way first!). The plunger was definitely sticking in the down position, gunked with carbon, so I cleaned it very well and got it working real smooth, put it back in with a new gasket, no change in symptoms.

The car has plenty of power, always starts.

Read the codes sticky and here's what it gave me:
P070 Intermittent TPS signal
P095 Stall detected
No other codes

Does this sound like a throttle position switch or the Idle Speed Control Motor? From reading these forums the TPS is a quick easy change. Should I try that first?

This forum is awesome!


04-01-12, 10:57 PM

Based on those codes, I'd replace the TPS. Also give the TB a good cleaning.

04-16-12, 05:10 PM
Thanks Ranger! I changed the TPS and gave the TB a good cleaning and it eliminated the stalling and cured the "missing" and surging about 90%. Also, no codes returned. There is a great post here, http://tinyurl.com/7o6vb29, and I wanted to clean the IAC while I had stuff apart. This TB is different than mine and does not have the IAC pictured. I don't even see this part anywhere on my TB. I think I can get it running 100% if I go back and clean the IAC but where is it on my car?

Faded Crest
04-16-12, 05:52 PM
Your car does not have an IAC, it has the older style Idle speed control motor which has the stop screw the presses against the throttle cable assembly. When these go bad they cause erratic idle and stalling as well. But it sounds like you have it figured out. The car isn't due for a tune up until 100k, but even though it has low miles the wires could be dried out from age. That might account for the last 10% of your problem if you have not replaced them yet.

04-16-12, 10:44 PM
GM switched from the ISC motor to the IAC valve in '96 I believe.

04-17-12, 12:20 AM
Ok, thanks guys. I've read here that people who change the ISC motor have to make their car "relearn" the correct idle. If I change mine do I have that same situation?

Faded Crest
04-17-12, 12:29 PM
I wouldn't touch it if your idle is fixed. It is a complicated thing to re-install it. You have a complete procedure you have to follow through the diagnostic center. It's not necessarily difficult with the FSM, but pretty much impossible without it. It will not completely learn on it's own.

04-23-12, 09:11 AM
Ok, it looks like I replied too soon. I've driven the car about 200 miles since my last post and yesterday it stalled twice. The only code I get now is the P095, stall detected. Is the idle speed control motor the only other part that could be causing this?

04-23-12, 05:56 PM
My PA would die randomly at slow speeds, never did throw a code, it was the TPS. I would try and locate a real time OBDII scan tool and watch it or test it. Basically it should have a very smooth change in voltage, any blips or drastic changes and its bad. Should be able to Google TPS testing and get more than enough info(that's what I did).

04-25-12, 09:39 PM
Thanks but I already tried the TPS and installed a new one, no change. I guess I'm changing the idle speed control motor this weekend.

05-05-12, 10:34 PM
Ok, changed the idle speed control motor tonight. I was real concerned about the high idle relearn procedure. When I installed it, even with the adjustment screw all the way in the TB butterfly was open about 1/64". I reconnected the battery, started it and it idled just fine.
I used Ranger's procedure and let it idle for 15 seconds, shut it off for 15 seconds, the restarted and checked for proper idle. I can almost say it was plug & play. It's definitely working, I can hear it find the sweet spot when the ignition is turned on.

At any rate, I drove it about 45 minutes and no stalls or other symptoms so it MIGHT be fixed but I've thought that before. While it had it apart I thoroughly cleaned out the TB for the SECOND time.

I'll repost and let everyone know my findings, hopefully my experiences will help someone else.

Thanks all.