Strange thing happened today, I was at a stoplight when all of a sudden my idle starts to surge, my car jumps up ahead, and i mash the breaks, then it revs up again and then down. next stoplight: same thing, but this time the car stalls completely. I put it back in park, started up the car, and it ran fine, but I noticed that it surges sometimes still. What could be causing this? TPS? I've been getting really crappy mileage lately too, could this be a cause?

 

Is it more like a shuddering, kinda like when on a manual car you forget to release the clutch while coming to a stop? I*think*the ECMs have some kind of stall recovery in the code, so when you get a stuck TCC, it could behave like you're describing, but what do I know, I row my gears! You could disconnect the TCC connector and see if it goes away but word of caution, been told 700R4s need the lock up to prevent burning up the clutches. stew

 

You're probably right!

Here's what to do, courtesy of Vader.

TPS Idle Adjustment

Vader
Moderator

Setting TPI idle -- the ECM controls the idle speed via the IAC. The mechanic sets the minimum air position of the throttle plates so that the ECM can do its job correctly.

The only correct way to "reset" the idle speed is to reprogram the ECM PROM. Until that is done, the ECM will try to maintain idle speed at the target idle set in the BLM tables. You may be able to get it to idle faster by changing the minimum air position, but it's going to raise hell with the ECM eventually.

Throttle Minimum Air Position

Tools needed:
1. Torx driver # T-20
2. Paper Clip
3. Small Punch
4. Tachometer

GENERAL NOTE: The engine should be at normal operating temperature before performing any adjustments. Never rely on the dash mounted instruments for diagnostics and adjustments. The oil pressure and temperature gauges and the voltmeter and tachometer just aren't calibrated accurately enough for diagnosis, but are a relative indication for monitoring the vehicle while driving.

For this adjustment, the transmission will be in DRIVE while you're under the hood. You will need to securely set the parking brake and block the drive wheels. It would also be a good idea to have an assistant hold the service brakes while you perform the adjustments.

In order to successfully complete the adjustment, the IAC air passages and pintle need to be clean. The throttle plates and bores need to be clean as well. If this is not the case, you'll need to remove the air cleaner from TBI engines or the intake air bellows from TPI engines to gain access to the area to be cleaned. A spray-type carburetor cleaner works well for this. Cleaning the IAC passages on a TPI/MAF engine will set a DTC, but we'll be clearing that later. With the engine idling, direct the spray cleaner into the IAC air passages and around the throttle plates. Shut off the engine and continue cleaning the throttle plates by opening the throttle manually. Once everything is satisfactorily cleaned, replace the air bellows on TPI engines. Many times, this alone can solve IAC/idle speed problems.

If this doesn't solve the problem, you may need to remove and clean the IAC stepper motor. If the IAC appears to be clean and functioning properly, continue with the adjustment procedure.

Idle Air Control Cleaning

You can remove the IAC and service it. Remove the electrical connector from the IAC. Unscrew the IAC unit from the throttle body.

You can gently rock the pintle back and forth and allow the spring to extend it until it comes apart in your hands. Clean everything with lint-free cloths and a mild solvent. Harsh solvents can affect the insulation of the stepper motor coils. It's generally the dirt and buildup on this worm shaft that causes sluggish IAC operation.

When the worm gear on the pintle shaft is clean and dry, apply one drop of clean light oil to the shaft and work the pintle back into the rack gears of the motor by the same rocking motion. It takes a while to get the pintle back into the worm gears, but you'll get it. It is important to get the pintle fully retracted into the housing so that the pintle is not forced against the gears when reinstalling the IAC unit in the throttle body.

While the IAC is out, clean the air passages in the throttle body. The oriface in the TB where the IAC resides is the seat that the IAC valve closes against, and it can accumulate a lot of carbon, dirt, and debris. The easy way to do this is with carburetor cleaner and a small stiff brush.

When everything is clean and dry, replace the gasket if it is damaged, apply a little anti-seize to the threads, and torque the IAC to the proper specs. (13 ft/lb for '85-'89 , 30 in/lb for 1990-on.) Proceed with setting the TPS and minimum air position.

Locate the Assembly Line Diagnostic Link connector under your dash panel. Remove the cover if it is still there.

Cut and form a paper clip into a "U" shape. Insert the clip ends into the ALDL in the 'A' and 'B' sockets.

Turn on the ignition, but DON'T start the engine. This will force the ECM into its diagnostic mode. Wait 30 seconds to allow the IAC pintle to fully extend. With the ignition still on, go under the hood, remove the electrical connector from the IAC, then turn off the ignition and remove the paper clip jumper from the ALDL. With the IAC pintle fully extended (closed) all idle air will be controlled by the position of the throttle plates. Some manuals indicate that the EST bypass connector should be disconnected for this procedure, while some make no mention of it. While timing is a factor in idle speed, the EST should only operate as a function of engine RPM, temperature, and detonation sensor inputs. To remove all doubt, disconnect the EST bypass connector is your car is so equipped. Some TBI and V-6 engines do not have this bypass connector, and therefore must be set with no regard to the EST system. The EST can be bypassed on some cars by grounding the diagnostic terminal at the ALDL and continuing with the procedure, but the fuel mixture will be skewed to the rich side, affecting idle speed as well. In any event, the minimum air position idle speed range is wide enough to allow for some variations. As always, it is best to consult your service manual for the exact procedure for your system.

Locate the Torx screw on the left side of the throttle body. It may be equipped with a protective metal cap from the factory. This was intended to discourage adjustment. If the cap is present, use a small punch to knock it out. Once the screw is accessible, start the engine and place the transmission in DRIVE. Adjust the throttle stop to obtain 400-450 RPM with the transmission in "DRIVE" on an automatic transmission car, 450-550 in neutral on a manual transmission car, rotating the Torx screw clockwise to raise speed and counter-clockwise to lower speed. Once the idle RPM is set, place the transmission in PARK and turn off the engine.

Re-connect the electrical connector onto the IAC. Start engine. Idle speed should be governed by the ECM at approximately 600-650 rpm in "DRIVE" (for unmodified cars). Idle speed in NEUTRAL or PARK is less significant, and will be higher.

Throttle Position Sensor (TPS)

Tools needed:
1. Digital Volt-Ohm-Meter (VOM)
2. Breakout jumper wires or probes (make your own)
3. AutoXray, Diacom, or similar scanner will replace the VOM and jumper wires.

Turn on ignition, but don't start the engine.

With a diagnostic scanner: plug in the scanner and read the TPS voltage. It should be 0.54Volts +/- 0.07 VDC.

Connect the VOM to the TPS electrical connector terminals ‘A' and ‘B'.

With a breakout jumper: Disconnect the electrical connector from the TPS. Install the breakout in-line, between the TPS and wiring harness connector. Connect the meter probes to terminals 'A' and 'B' on the connector. (‘B' is the positive connection, ‘A' the signal ground, or negative.)

With probes: If you have very slender probes on your VOM, you can back-probe the TPS connector while it is attached to the TPS. If you have made probes of large dressmakers pins or a similar item, you can back-probe the connector as well. Connect the meter probes to terminals 'A' and 'B' on the connector.

Turn on the ignition to read the TPS output voltage at the idle position. The reading should be 0.54VDC +/- 0.07VDC. The ideal is the center of the range, 0.54VDC for a stock engine. To adjust the output voltage, loosen the two Torx screws holding the TPS to the throttle body, and slightly rotate the TPS up or down, reading the voltage until it comes into specification. Tighten screws. Using the throttle lever, rotate the throttle to WOT (wide open throttle). The TPS voltage should be over 4.0 volts. Close the throttle again, and then slowly open it to WOT, observing the voltage reading. It should increase progressively and in a linear fashion. If it sticks or jumps or falls off at all while doing this check, the TPS sensor may be failing and could be a cause of stumbling and driveability problems.

After achieving the desired setting, turn off the ignition switch. Remove all jumpers or the scanner and reconnect the TPS connector as required.

Reinitializing the ECM

If you set a DTC during the procedure, the SES light should be illuminated on the dash. This ECM retains DTC data for the previous 50 engine starts, so the codes will eventually be cleared. If you want more immediate results, after shutting down the engine disconnect the negative battery terminal for five minutes. This will clear the ECM of all diagnostic trouble codes. Clearing the ECM also clears any data learned about your engine, and clears the radio presets. If you have a Delco-Loc or Theft Loc II radio, make sure you follow the procedure to unlock the radio protection before disconnecting the battery. This five minutes is also just about long enough to clean both battery cables. Reconnect the battery. When you first start the engine after clearing the ECM, the engine will operate with base parameters programmed into the ECM PROM. These parameters may not be optimum for your engine, but the ECM will enter a Block Learn Mode soon after the engine is warm and enters Closed Loop Mode. The ECM will write new data tables specific to your engine and will eventually rely on those tables instead of the base tables of the factory program. You can expedite this process by driving the car for 20 minutes under varying conditions to allow the ECM to initialize. Or you can wait and drive the car normally at your convenience. The BLM tables are constantly being updated as sensor input ranges change, but the greatest change will occur within the first twenty minutes of Closed Loop operation.

 

Interesting, so our cars are only supposed to idle 500-650ish? Currently in park the car will idle at 1300, and in drive at 800 rpm. Thanks Ed.

 

Does SES come on?

 

Alright, so I hooked it up to the scanner, and the TPS voltage was right on at .54, turns out that my uncle said that whoever installed the aftermarket radio didn't connect the negative terminal of the battery correctly, so the car was losing voltage over the course of time causing irregularities in the computer... Does this sound like a good diagnostic to you guys?

 

If the battery is not fully charged, the car will have weird problems; if the battery won't hold a charge, those problems continue. There might also be excessive parasitic electrical drain caused by a malfunctioning component or wire.

Tests for those problems are easily done and are listed in service manuals and searchable in TGO.

However, the "surge" problems are well-documented here and a search turned up about 170 responses in the TPI forum. Most posts referenced the Vader Tuneup and since your engine idle changes from in-gear and neutral, it appears logical to continue the TPI tuneup process. Both of our 5.7 TPI cars idle at the same speed, regardless of in gear, in neutral, or with AC on/off, and the engine takes a couple of seconds to find the correct stable idle speed.

In most cases, surging is caused by vacuum leaks, dirty IACs, or someone trying to adjust TPI idle speeds by merely turning the adjustment screw "carb style". Gotta follow the proper process to setup the TPI.

 

alright, the problem arose again today, except now im getting a SES light whenever i turn the car on, it goes off periodically then comes and goes... sort of strange, also, a wire that was suppsosed to be attached the the neg battery cable apparently broke off the terminal, and im not too sure what it was for...

 

Hook it up to the scanner again and see what code its spitting out for the SES light. Also, might wanna trace that wire and see where it goes. If it was attached before the problems started that might be the culprit right there.

 

well that wire broke off today, when i was trying to remove the battery and replace it... long story... but ill definately hook it up to the scanner again.

 

Use a volt meter to test TPS. An analog one if you have it. KOEO (Key On Engine Off) slowly step the throttle or pull the cable and watch for a smooth rise in TPS voltage signal. Any skip or jump is bad. That being said, I doubt it's TPS.

It could also be IAC if it's dirty or has faulty wiring. Ed listed a few other things to check.

Shawn's right- get that DTC code now that it's saved. DON'T disconnect the battery until you pull that code.

I didn't read that wonderful write-up by Vader, but I have it printed and will get to it soon. If you follow Vader's advice, you should be set.

Let us know how it goes. We got to get your car running well for the track!

Scott

 

while running my A/C today for a little while in park right before i got out of my car, a cloud of steam erupted from my hood when i turned the ignition off, and when I tried to put in some more coolant/water mix, it just poured right out of the drivers side of the radiator... is there a way to fix this, or do i need a new radiator?

 

Coolent temps spike when the engine is turned off, sounds like the radiator blew out. Two months ago the radiator in my '87 5.7 did the same thing downtown in traffic, so I replaced it with a GoDan 433918 stock replacement radiator at Checkers for $149.99. It's a two-core aluminum with plastic side tanks, just like the original and has a lifetime warranty.

Although there is a difference in opinion about what is the "best operating tempurature" for 3rd Gen cars, IMHO having weak little unshrouded fans come on at 220 degrees, only 20 degrees before boilover, is a sure-fire way to stress-test the cooling system.

In fact, a good way to determine if the cooling system is in good shape is to warm up the car, then park, turn on the AC, and run the engine at a fast idle for 20 minutes. If all is well, the car won't overheat -- if it does, then there's fixing to do...

If you're in traffic and the cooling system starts to boil over, turn off the AC and turn on the heater full blast. You'll suffer, but in all likelihood the car's temp will start to come down [unless of course the radiator has already boiled over losing some coolent].

Oh, and one more thing -- always carry a spare plastic heater diverter valve in the car, 'cause someday it will break and put you on the side of the road for a tow-job and nobody will have one in stock. Having a spare to change only takes 10 minutes and a screwdriver. It will happen, trust me...

 

Check the plastic tanks. It's common to crack along the driver's side. You might not see it until it's pressurized, but if it's dumping out you can probably ID it right away.

You <i>could</i> get it fixed at a good radiator shop and have them to put metal tanks on the side, or just pick up the one Ed mentioned with the lifetime warranty. The plastic will be fine <b>as long as the rest of the system is working correctly.</b>

Either way it's coming out of the car, so go ahead and get your gaskets and probably a lower temp t-stat.

Scott

 

Well, it is leaking from the plastic tank on the drivers side, at the seam where the metal meets the plastic... So far, all i've done to temp fix it is epoxy sealer... In the end though, would a new radiator be worth it more than a simple repair of the current one?

 

If the radiator is old, funky and the cooling system not well maintained, it's best to start with a new one ... especially in 3rd Gens that as a group have systemic cooling problems caused by a marginal design.

 

I'd change the fan's turn on temps in the PROM to a lower temp, cuz simply changing to a lower temp thermo won't do much unless you got airflow thru the radiator. And the idle speed is supposed to be slightly higher in park/neutral and when the A/C is on. There are specific values labled "park/neutral idle speed adder" and "A/C enabled idle speed adder" in both the $6E and $8D code. These values are adjustable in the constants table. Some masks display this value in RPMs while others display it in IAC motor steps. Either way, GM tuned it to increase idle speed in either situation by about 100 rpm for park/neutral, and from 50-100 for A/C enabled... different masks used different values. If you're running an electric water pump tho... then these values can be set to zero. Otherwise, cars with belt driven pumps may benefit from the additional flow.
Also, the ECM is EXTREMELY sensitive to inadequate grounds. Like Ed said, you'll have a bunch of computer related problems without a good ground. It'll throw codes that don't really make sense, after you check that the indicated system works fine. The first time i moved the battery to the back, i grounded the negative terminal to the chassis figuring that it would be a good enough ground, but that turns out not to be the case. I fried the ECM, and had to run a big wire from the negative terminal, straight to the engine block.