Goofy

'88 GXL Automatic.

Coming home last night when I'm going about 20mph and just barely touching the gas, the car kinda hops forward and back, forward and back. Same thing happens at 60mph if I'm barely touching the gas. (Never got to test it at other speeds.)

Going to work today, same thing at 20mph, except that it stalled out at one stop and almost stalled at another.

Also, when I let of the gas, the transition from powered to unpowered forward momentum feels like I drove into a deep puddle of water, whereas I'm used to it being pretty smooth.

I just changed my belts (AC and PS included) and I think I may have overtightened them. Other than that, I was fiddling with my 5/6 ports (I could push the rear one in by hand, but not the front one.)

Also, when changing the alternator belt I accidentally let the positive contact hit ground for a split second while the radio was on, but it was fine as soon as I took it off. Then I disconnected the battery at positive to continue progress. (The alternator bit wasn't exactly my fault, since someone mickey-moused the positive connector making it really easy to hit stuff.)


Other than that (I know that's a lot of possible faults) I don't know what's changed.

So, my first, and main, question is: Could overtightened belts cause this?
Second: What else would cause throttle surge at the cusp of load and coast?

Thanks,
Goofy

Icemark

TPS is broken or out of adjustment

86gxl_fc

could be some kind of vacuum leak. mine did that when i found a crack in my LIM. ran alot better in the top end, but seriously sucked ***** on the low end, had a really bad rough idle.
you didnt mention anything about the idle so i guess a vacuum leak is probably out of the question.

SureShot

Yes - the TPS is the most likely.

If you're rolling & the TPS is telling the ECU the throttle is closed, the ECU cuts fuel.

Also a partly clogged/dirty injector could be leaning the fuel at low throttle.

88rxn/a

iTrader: (6)

man is that TPS a pain to get just right!!!!
lol

Goofy

I'll assume it's the TPS, adjust it tomorrow after work, and update. Thanks, everyone.

SureShot

Here ya go - TPS test & set:
Using test lights or voltage at idle readings will get your idle setting perfect, but you could still have a worn out TPS resistor.
-The golden test:
Unplug the TPS connector.
Clip a cheap analog (needle type) VOM on the orange & black pins.
Set it to the 1K Ohms scale.
Hold off the throttle & work the short range TPS plunger in & out.
You should see a smooth sweep from ~0 to ~5K ohms.
Any bad spots or drop outs in the stroke - it's bad & will give fuel cuts at part throttle.
(Before you toss it, try spray contact cleaner between the sleeve & plunger.)
- Then set it:
Find the fast idle (warm-up) cam & push it back so the throttle sits on the hard idle stop.
Adjust the setting to 1K ohms.
While holding off the fast idle cam, open & close the throttle a few times to see that the 1K setting repeats.

Goofy

Well, I checked my tps using this reference (page 4A-50).

I read 1k to 5k on A-B nice and smooth, but I read 5k to 0.5k on A-C.

Also, I no longer surge at idle and my throttle surge happens squarely at 1500 RPM in park.
If I disconnect my TPS I idle at about 550 RPM kinda rough, but I range up through the RPM range to 3k fine. (I guess I failed to check if there were any surge spots, but didn't notice any.)

I only adjusted it (not that it needed much) using the single screw that's usually covered by a cheap piece of plastic (not the rubber-capped screw on the plenum).

Any more ideas? Do I need to replace the TPS to fix this 5-.5k problem? Is there a typo in the FSM and it should read 5-0.5k, not 5-5k?

Thanks,
Goofy

Goofy

Update after driving it home: It's unstable at idle again. I find that odd since it was quite solid before I drove it home. I wasn't getting any surge at cruise, but I was cruising at 75-80, not 60.

Goofy

Should I just turn up my idle to about 1k until I have this properly resolved? Should I unplug my TPS? Should I do both?

Goofy

Can I get a confirm that I need to replace my TPS since my A-C connection sweeps from 5k to 0.5k even though my A-B connection is fine from 1k - 5k?

I guess I'll also start looking for vac leaks.

synesthete

Try unplugging your o2 sensor temporarily. I was having this issue while i was cruising down the freeway about 80 with my foot just barely on the gas, and i would here this slow rhythmic pulsing from the exhaust, very annoying, didnt actually feel any change in momentum or anything though. Unplugged the o2 sensor and it went away completely.

Goofy

Would a bad O2 sensor cause a bad idle though?
And why does no one ever state that the A-C connection on the TPS needs to be checked? And why in the world would it be there instead of just a resistor if it's just supposed to read 5k instead of going from 5k to 0.5k?

Goofy

Could this all be because of a bad positive cable connection to my battery?