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Discussion Starter · #21 ·
100 miles down and she's doing better, not perfect but better. Usually hanging around 1500-1700 rpm before getting back to normal in about 15-20 seconds. I do not know if this is related but I filled her up with gas and it started doing way better (intermittently) going right back down to idle 700-900 with no "bouncing" or "hunting" be curious if there is something there. The cardboard trick lets the trooper warm up much faster. Thanks again for the help Ill keep everyone updated if I ever find a permanent fix or a glaring problem.

- Jon
 

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Sounds like an improvement. You also might try running some fuel system cleaner in in. Gumout Regane Hi-Miles is cheap at Walmart and has a high level of the carbon-cleaning solvent PEA. The Hi-Miles stuff with a top-end lube is good for our poor ol' engines.

https://www.walmart.com/ip/Gumout-Regane-High-Mileage-Fuel-System-Cleaner-6OZ-510023W/16888905

And just now found something that I'd never seen before, a GM TSB on diagnosing intermittant engine revving, the procedure to fix it is pretty simple, so it might be worth trying it out:

Diagnosing Intermittent Idle Speed Increases
Group Ref.: Engine Fuel & Emission
Bulletin No.: 476510
Date: May, 1994

INFORMATION

SUBJECT:
DIAGNOSING INTERMITTENT ENGINE IDLE RPM INCREASE


MODELS:
1988-89 BUICK CENTURY AND REGAL
1988-89 CHEVROLET BERETTA/CORSICA, CAVALIER AND CELEBRITY
1988-89 OLDSMOBILE CUTLASS CIERA AND SUPREME
1988-89 PONTIAC GRAND PRIX AND 6000
WITH 2.8L ENGINE (VIN W - RPO LB6)

1989-93 BUICK REGAL
1990 CHEVROLET CELEBRITY
1990-92 CHEVROLET CAMARO
1990-93 CHEVROLET BERETTA/CORSICA
1990-94 CHEVROLET CAVALIER AND LUMINA
1989-93 OLDSMOBILE CUTLASS SUPREME
1989-91 PONTIAC 6000
1989-93 PONTIAC GRAND PRIX
1990-92 PONTIAC FIREBIRD
1991-94 PONTIAC SUNBIRD
WITH 3.1L ENGINE (VIN T - RPO LHO)

1991-94 CHEVROLET LUMINA
1991-94 OLDSMOBILE CUTLASS SUPREME
1991-94 PONTIAC GRAND PRIX
WITH 3.4L ENGINE (VIN X - RPO L01)

1993-94 CHEVROLET CAMARO
1993-94 PONTIAC FIREBIRD
WITH 3.4L ENGINE (VIN S - RPO L32)

1994 BUICK REGAL AND SKYLARK
1994 CHEVROLET BERETTA/CORSICA
1993-94 OLDSMOBILE CUTLASS SUPREME
1994 OLDSMOBILE ACHIEVA
1994 PONTIAC GRAND AM AND GRAND PRIX
WITH 3.1L ENGINE (VIN M - RPO L82)

The following information may assist in the diagnosis and correction of an intermittent increase in engine rpm with closed throttle (accelerator pedal not depressed). Typically there is no malfunction indicator light associated with the condition.

The engine control system sensors are supplied a 5 volt reference signal to ensure properly scaled readings to the engine control module (ECM). If a large current draw flows through the circuit supplying the 5 volt reference, the input signals, as read by the ECM, will be skewed low. The ECM program will store an incorrectly low throttle position sensor signal as zero. If the reference voltage returns to normal, the ECM will interpret the resultant high throttle position sensor signal as an open throttle and idle air control steps (throttle follower) will be added accordingly, causing an increase in the engine rpm at idle.

The A/C pressure transducer has been found to be especially vulnerable to shorts during the engine crank process. Electrical wires in the engine harness that are unprotected and rub on structural members also will cause the problem.

Inspect all wiring and sensors associated with the 5 volt reference signal for shorts and correct as necessary.

If the vehicle also has a condition associated with the air conditioning system, diagnose and correct as necessary.

With a Techline Diagnostic Tool, read the throttle position sensor, manifold absolute pressure sensor, and A/C pressure transducer voltage with the key on-engine off.

If all three voltage readings are skewed below their normal ranges, inspect the A/C pressure transducer.

If all three voltage readings are within normal ranges, disconnect the battery for one (1) minute, reconnect and start the engine. If the increase in engine rpm at idle condition is gone, inspect the A/C pressure transducer.

NOTE: On the LB6 (2.8L VIN W), LHO (3.1L VIN T) or L01 (3.4L DOHC VIN X) engines, If the ECM Is without battery power for any reason, then the Idle air control valve (IACV) position information for a stable satisfactory engine Idle Is "lost" and replaced with a default value. To correct the IACV position Information, perform an Idle relearn procedure using a Techline Diagnostic Tool. You can also manually relearn the Idle by following the procedure below.

1. Remove battery power for one (1) minute. Restore battery power and place air conditioning controls (if equipped) in the "off" position.

2. Firmly apply the parking brake and block the drive wheels. Start the engine, shift the transmission to drive for automatics and neutral for manuals.

3. Allow the engine to run until the engine cooling fan has cycled once, or a maximum of 10 minutes.

4. Turn the ignition key to the "off" position for at least 5 seconds.

5. Repeat Step 2.

6. Allow the engine to run for at least five (5) minutes.

The correct IACV values for proper idle control will now be stored.



Makes a lot of sense, don't it! See, learn something new every day! 馃樇 馃槑
 

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Discussion Starter · #23 ·
Well I am back. I have been driving the trooper for about 4 months now, she still oscillates when I take it out of gear but only sometimes. Other times she goes straight back to 900 rpm and runs really solid.

I am going to go down the ALDL route and see if I can figure it out.
 

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Discussion Starter · #24 ·
Got the ODB1 Cable in and hooked her up. I am getting no sensor readout. Any thoughts on what I am doing wrong? I know the ECM is talking somewhat because the RAW data is populating some fields. Any help would be great.
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Here's a fairly recent thread where the O.P. was having issues getting his WINALDL working, we finally worked-thru it with some good results. There may be something in there that you'll find useful:

 
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Discussion Starter · #26 ·
Got the WIN ALDL figured out. It was definitely the baud setting of 4800. Now I have the .txt file. Not exactly sure what to do with it but I can now see that my idle is high and I can see the surging in the engine. What I need help with is interpreting the data.

see attached.
 

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If you go in and disable the IAC (with the pintle fully closed) via the IAC and TPS procedure, with the IAC unplugged, do you still have a stable idle? I'm not so good at reading a raw data table but looking at the IAC pulses, it's definitely a cyclic problem. Something is causing the ECM to tell the IAC to open, close, open, close, ad nauseum.

If it will still idle stably at 750 or so with the IAC disabled, you at least know that the problem isn't mechanical. It has to be sensor/ECM driven.

I looked back in the other thread, and Mike sent his data to the WINALDL guy (the one who wrote the free program in the 1st place). So maybe try that, he might be able to give you an idea about what's causing the surge. Could be a lean surge, I dunno. Something it doesn't like, for sure.

What was your Temp sensor reading, around 195 +/_ whatever? The engine must be up to full temp in order to get into Closed Loop, and sometimes if it's idling too long the O2 sensor will cool down & the ECM falls out of Closed Loop anyhow. There was one value that ran from about 96 to 164 that could be temp but IDK? In Notepad I didn't have any luck getting the headers aligned with the data entries, so I'm just guessing which column does what. Is this exportable into Exel or maybe some other spreadsheet so it's better viewable?

HTH & keep us posted..........ed
 

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OK, I was able to open it with Excel and get each data row properly formatted. The coolant temperature is definitely low. The ECS could be bad, or just going out-of-calibration. Or, what 'stat do you have in the engine? It should be 195F. A cooler or malfunctioning 'stat won't bring coolant up to operating temp, and the ECM would interpret that as a cold engine and raise the idle speed.

Can't go wrong with a Stant Superstat:



Not too sure about the O2 sensor, either. Inconsistent readings and all over the map. Maybe not warm enough exhaust? The sensor should cycle its voltage up and down as per changes in air/fuel ratio.

I'll attach a temp vs resistance chart for the temparature sensor, it's the one screwed into the center of the intake manifold, just forward of the TBI.
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Discussion Starter · #30 ·
The STAT might be original to the trooper for all I know. It seems like it will never get above 178 F. Do you think this could be the cause of the engine surging? The O2 looks all over the place, it is a new sensor (not heated). Also I am getting a engine code 32 for EGR (also new). I might have to get back to the vacuum diagram and just replace every stinking hose. Here is the latest data.
 

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Yeah, make sure vacuum hoses are routed per the sticker on the underside of the hood. It's not uncommon on these to see the TBI base gasket leak, you can spray WD or carb cleaner around the base of the TBI and see if the engine speed goes up.

The EGR code is most likely a result of all the engine surging. The ECM checks EGR function by cycling the EGR open and then seeing the corresponding changes in the MAP and O2 sensor readings. You have to be driving a certain amount of time in Closed Loop before the ECM will launch an EGR test.

Seems like things are more stable when warming up, then before it gets to the highest temp, it starts to surge. Weird.
But it should be getting to at least 195F; I'd change it, or at least check/test the thermostat.

Definitely send the data to the WINALDL guy, he should be able to determine what's going on.
 

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Discussion Starter · #32 ·
Ok I have replaced the stat. Turns out there was a 160 degree stat installed which is why the engine wasn't getting to temp. I replaced it and now it gets to temp nicely and idles perfectly. However the surging is still happening and now I have codes 32/33/34 here is the latest file.
 

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Well, since you replaced pretty much all the sensors, I wonder if the EGR controller is going screwy. The MAP code might be due to the vacuum fluctuations.

Try pulling the EGR valve's vacuum line and plug it. See if it still surges. If so, the EGR controller is probably porting vacuum to the EGR valve at the wrong time, it's only ever supposed to recirculate exhaust gas under certain conditions when the engine is running down the road.

Something else to try, if you have a vacuum gauge, connect to the EGR vacuum line after you unplug it from the EGR valve. That'll tell you if something strange is going on. There should be Zero vacuum on the EGR at idle.

Nice to see it warm up to almost 193 Deg then stabilize and hold at 187.3. Pretty steady!

Look at the IAC counts once the temp stabilizes; it's Zero. So the IAC is not letting any extra air in.

So, my pea brain wonders, how can you get surging idle speed if the air going into the engine is constant?

Could very well be the EGR! Which of course will cause intake air to change and will vary the vacuum that the MAP sensor sees. Sometimes it's hard to figure out the Chicken or the Egg.

Note that the BLM (long term fuel correction) holds pretty steady at 112 but then it goes to 126 and then back down. I expect this is a response to a change in manifold vacuum.

Well, there's something else to check. If the EGR troubleshooting doesn't pan out, I'd definitely send this data to the WINALDL Dude. With stable temperature and almost-steady idle, maybe he can figure out what's going on.

BTW, even a new EGR valve can be bad, and if it doesn't seal properly or is sticking, you could get a low idle or stalling. Maybe not a surging idle, though. You could go so far as to make a block-off plate and install that with a gasket. That would rule out the EGR entirely.
 
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