spot_skater

Hey guys.

If any of you read my last post about a surging idle, you'll have an idea of what's going on.

A few nights ago, it was FREEZING cold, and I had to drop my girlfriend back off at her house. Started up my car, she started just fine, drove to her house, dropped her off, no problems. Before I went home I decided to get a pack of cigarettes. On my way there, the problem started. Coming to a stop sign, clutch in, on the brakes, my idle started to become bouncy. It would surge from about 1400-1800 RPM. Remember, this happened out of nowhere. I hadn't changed driving habits, was shifting at ~2700 rpm, not driving it hard, and coming to a stop sign this problem came up.

I just adjusted my TPS to 1000 OHM at 0 throttle, checked to make sure it's in spec, and it is. My O2 sensor is about a month and a half old, just replaced it, and it is reading good voltages. My coolant sensor is good. On initial start up I watched BAC slowly back out of it's diaphragm, which lowers the idle on cold start assist (Which IS still attached, and working). There are no vacuum leaks, I double and triple checked for those, too.

I installed a RB header recently, and the previous owner had an EGT gauge in first, and I semi-plugged it... would an exhaust leak cause this?? The leak is AFTER the O2 sensor. The timing is stock and in spec, and prior to these issues my car was running great. I had driven it with the new O2 sensor for about a month and a half, no problems. Same amount of time with the header on, as well.

I read that maybe the linkage along the throttle plates may be sticking, in the TB, I will give that a check shortly.

I'm kind of stumped here, mostly because it just popped up out of nowhere.

If any of you guys have any directions to point me in, I'd appreciate it.

Thanks,
James

EDIT::: The Thermo Unit connector on the Oil pan is disconnected right now. I thought that might have had something to do with it, so I waited to run the car without ******* with any adjustments for a few days, when the temps came back above freezing. After a 3 day wait (today), this problem was still there. It's around 50-60 degrees out.

Icemark

set the TPS at the ECU. I have had a couple that had the same surge, and it was TPS with corroded connectors inline. Setting the TPS at the ECU solved the problem.

Another way to check is to just crank the TPS up one or two turns, or down oen of two turns. If it solves it, then again it is a mis-adjusted TPS.

spot_skater

I tried turning the TPS adjustment screw while the car was running, and warmed up. I couldn't get it to idle/surge any lower than 1300 RPM. To be a little more clear, it would surge from around 1300-1600, at the lowest RPM. Turning the screw any more in or out only made it worse (surge at a higher RPM).

I will look up ECU pins and wiring diagrams now. To adjust through the ECU will it be the same specs as off the TPS, using resistance? Or will it be using a voltage signal?

Thanks,
James

Icemark

Just unplug the ECU and check the TPS resistance there, and yes set again for 1K Ohms

spot_skater

I tried to check the resistance from the Red and Blue Wire on connector EM 31 (the Throttle Sensor Wire) to it's corresponding Pin, and I couldn't get a reading. I am using a Blue Point Digital Multimeter, and it's set to read Resistance in the correct range. There is definitely a signal coming FROM the connector, I checked the resistance between the Red/Blue wire to other Pins on the ECU, and I was able to get readings. When I had to move the car just now, above the surging idle RPM (1300-1600) everything is smooth, but once it comes back down again, the surging begins.

Do you think it's possible the BAC is sticking? I can watch the plunger move, and it moves freely when I push it, and upon warm up it is nice and slow.

Could a skewed O2 sensor wire give false readings? I looked under the car today and I noticed that some of it was dirty, corroding and overall really shitty looking. I say under because I'm running an RB header, and the O2 sensor bung is closer to the presilencer than the block.

Stumped.

James

Icemark

O2 doesn't work until warm.

Unplug the BAC to confirm if it is the BAC or not by checking the AC voltage on the wires does not change as the car warms up.

spot_skater

The car has been warmed up, and then kept warm throughout all of the tests.

I will check out the BAC tomorrow, it's getting cold and dark outside.

Thanks, Icemark.
I'll update as things progress (hopefully!)

James

Icemark

You can double check the TPS as the cause by just unplugging it as well. If it is the TPS, with the TPS unplugged the same problem will not happen.

spot_skater

That was going to be my first step, then I realized that the previous owner had the harness removed and soldered some wires in place of it. ********.

Not you, the previous owner.


James

spot_skater

UPDATE: I checked the TPS again, and adjusted it with the light method, it was in spec at the time. I checked the Idle adjust screw on top of the intake manifold, and it had no effect, so I put it back to the way I found it. I did find a vacuum leak, a rather obvious one...the hose to the pressure sensor had fallen off, reconnected it, it did not change idle.

I jiggled around the thermowax and fast idle cam, checked the throttle plates, and everythign looked good...weren't dirty or anything. By jiggling the fast idle cam and thermowax, I mean just that. I didn't take off the TB and adjust anything, just felt around looking for the screw, which I didn't find, moved the linkage around a bit. Then I reset the ECU by removing the neg battery terminal, stepped on the brake pedal a few times.

Started my car up, start up 3k warm up cycle began...it hadn't since this problem happened. She idled slowly down to 1500. Surged a bit. Drove the car about 1/2-3/4 of a mile down the road, came to a stop sign, and the idle was back to 750.

No surging whatsoever. I have to run, if any problems arise I'll keep you all updated. My thoughts are that the pressure sensor being disconnected may have thrown a code, and by resetting the ECU and reconnecting it it might have erased the code.

James

spot_skater

So I guess after resetting the ECU didn't really solve my problem. For the last few weeks it's been surging, constant. Did some tests on my pressure sensor and MAF, everything checked out. I ended up replacing my TPS from one off a GXL in a junkyard, re-adjusted everything, and re-wired it in... the previous owner didn't have the stock connector or harness there, so I cut that **** and re-soldered/re wired it, with connectors going from the TPS to the wires, adjusted everything and she is now stable at ~800 rpm. I also replaced the vac hose for the pressure sensor, which was rock hard.

Just an update for any of those who care.

Thanks for the help, those who did.

James

EDIT: Also, I checked the resistance values of the old TPS. They were off the charts. So it was indeed a bad TPS.