'94 Surging in gear at idle

[formul8]

Sometimes my '94 will start to surge at a stop in gear. If I put it in neutral, it stops and idles fine.

I am getting DTC 43 that I have been trying diagnose. Could this cause that?

Knock sensors are brand new.

 

[Toms007]

I'd sure like to know what's going on with 94 model Vettes. There have been several here in the last 5 months having very similar problems. Hope you can get this figured out.

 

[formul8]

Maybe the sequential injector firing isn't so sequential? Even on some other boards it seems '94s have the most idle problems.

 

[formul8]

This thing is weird.

The CEL went off, finally. Cars starts to surge even more at idle. Comes back on later, idles better.

It has done this a few times today. I'm stumped...

 

[Steve40th]

Disconnect battery for a few minutes, then see if code comes back. If sensors were just replaced, check wires and connections. Remember too Knock Sensors only get torqued to 14ft/lbs in the block.

 

[formul8]

I tried clearing the codes. This has been a problem for a while.

It did it again today. The CEL is off, then comes on after a while. Before, it would stay on all the time.

 

[nickyg]

I'd sure like to know what's going on with 94 model Vettes. There have been several here in the last 5 months having very similar problems. Hope you can get this figured out.

Yes, this seems to be an ongoing problem which I experieneced myself. After reviewing countless posts with people with the same issue and attacking almost virtually all areas, I finally solved the problem after I replaced the ECM with one from PCMFORLESS.COM with a couple of minor programming changes. Most noteably the changing of the on/off times of the cooling fans which keeps the car running cooler. My experience with this issue happened only after warm-up. Not to say that this is your issue also, but you have to go through a systematic diagnosis to zero in on it. If you have a factory service manual, great, if not, get one. It's the best investment you'll make for your vette.

 

[formul8]

I am thinking the PCM is the next step because the wiring is fine, both KS's are new and the CEL comes on when it warms up now.

The odd thing is, the coolant temp stays around 200-203 with the CEL off.

When the CEL comes on, which is always DTC 43, the fans kick on constantly and the temp stays between 205-209.

I am also thinking the o2 sensors need replacing because the gas mileage sucks!

These cars are weird...

 

[nickyg]

Probably a good idea to change your O2's depending on how much mileage is on 'em. I found this on DTC 43:

CODE 43
Trouble Code 43 indicates that there may be a malfunction in the Electronic Spark Control (ESC) circuit. ESC is used to sense spark knock (pinging) and retard the timing to eliminate it. A knock sensor (located at the rear of the engine block) sends signals to an ESC module which then signals the ECM that knocking is being detected. The ECM will retard the timing by as much as 20 degrees in 1 degree increments. A loss of knock sensor signal or loss of ground at the ESC module will cause the signal at the ECM to remain high. The ECM will act as if no knock is present, and may possibly result in engine damage, if there is detonation. Loss of the ESC signal to the ECM will cause the ECM to constantly retard the timing to its maximum. This results in sluggish performance and a Code 43. The conditions for setting this code are:
* Engine is running
* ESC input signal has been low more than 2.23 seconds
Typical causes for this code include:
1) Open or shorted knock sensor
2) Loose knock sensor
3) Excessive mechanical noise within engine
4) Improper or incorrectly installed PROM or CALPACK in the ECM or defective ECM
5) Intermittent open in the EST line to the ignition module

Hope this helps

 

[Toms007]

My code 43 was caused by the optispark not functioning properly. When the opti was changed for one that was working properly, my code 43 went away. Check the optispark for proper functionality. Actually it was just the Cap and rotor in my case.

Remember, I chased my Code 43 around for weeks, checking then changing the KSs and tracing it back to the ECM which was apparently working correctly before I had someone else look at it only for them to find the opti problem.

Oh and once I got it running correctly my gas mileage came back, almost 26mpg on a 400 mile trip last weekend.

formul8, if you decide that you need a new ECM I have one that will work...unless GMJunkie decides he wants to keep it.

 

[formul8]

NickyG- Thank you for that info!!!

The opti is my next stop. Maybe there is something wrong with that.

I did replace the grease on the ICM and cleaned the heat sink of all the gunk. The miss went away after that.

I just think it is weird that it now throws the code when warm. Maybe when switching from open to closed loop?

I'll have to run a scan and see what the o2's are doing. That might have to wait because I parked the car for the time being since I lost my job.

 

[Toms007]

NickyG- Thank you for that info!!!

The opti is my next stop. Maybe there is something wrong with that.

I did replace the grease on the ICM and cleaned the heat sink of all the gunk. The miss went away after that.

I just think it is weird that it now throws the code when warm. Maybe when switching from open to closed loop?

I'll have to run a scan and see what the o2's are doing. That might have to wait because I parked the car for the time being since I lost my job.

That's what mine was doing...as soon as it went into closed loop...bang the SES light would come on....Code 43. I would have sworn it was some sensor.

BTW I have a new (rebuilt/reman'd) ECM for a 94-95 with a 6 speed if you find that yours is bad, just let me know if you want it. I think I gave $100 for it. GMJunkie says it works great, but ECM wasn't his problem either.

 

[nickyg]

NickyG- Thank you for that info!!!

The opti is my next stop. Maybe there is something wrong with that.

I did replace the grease on the ICM and cleaned the heat sink of all the gunk. The miss went away after that.

I just think it is weird that it now throws the code when warm. Maybe when switching from open to closed loop?

I'll have to run a scan and see what the o2's are doing. That might have to wait because I parked the car for the time being since I lost my job.

Wow man- sorry to hear about the job. Hopefully downtime won't be long.
Another thing to check is your plugs and wires. Check for arcing in the darkness of a garage. Also the condition of the wires and connectors going to the coil. Sometimes it doesn't take much to create an open or an intermittant one at that. Age and heat are ememies of wires and vacume hoses for that matter. Our generation of vettes aren't exactly young chickens.

 

[formul8]

Wow man- sorry to hear about the job. Hopefully downtime won't be long.
Another thing to check is your plugs and wires. Check for arcing in the darkness of a garage. Also the condition of the wires and connectors going to the coil. Sometimes it doesn't take much to create an open or an intermittant one at that. Age and heat are ememies of wires and vacume hoses for that matter. Our generation of vettes aren't exactly young chickens.

Plugs and wires are brand new.

Sounds like mine is having the same exact problem as Tom's car. It starts to surge a bit, the CEL comes on and then smooth idle. The weirdest thing is engine temps. It runs 5 degrees hotter with the CEL and the fans on...

I would take the ECM, but mine is an automatic.

 

[Toms007]

Plugs and wires are brand new.

Sounds like mine is having the same exact problem as Tom's car. It starts to surge a bit, the CEL comes on and then smooth idle. The weirdest thing is engine temps. It runs 5 degrees hotter with the CEL and the fans on...

I would take the ECM, but mine is an automatic.

They can be reprogrammed for the correct transmission. I asked Junkie, he's not even sure if the program is different for an auto.

 

[formul8]

The computer in a '94 with an automatic is actually a "PCM" or Powertrain Control Module because the it controls the shifts with programming and electronic solenoids.

I don't think it will work.

 

[formul8]

Well, problem still happening.

It idles a little rough, then when it warms up it starts surging a little and struggling and then the CEL comes on and idle smooths out. H43 is the code that comes up. I cannot see how that can be the issue because the engine does not knock at all.

The exhaust is very rich on the drivers side. I am thinking o2 sensor?

This is driving me nuts!!

 

[Schrade]

Surging in gear at idle? What about when in neutral at idle?

Have you checked for a vacuum leak? Test procedure (should be done in closed loop) here.

 

[Hib Halverson]

What codes are set in this car's ECM?

 

[formul8]

Was getting H43, but put in a new o2 sensor on the drivers side and that fixed the problem! The old one was the OE and was caked in soot. It must have been very lazy, if working at all.

Still idles a little bit rough, but I need to take plugs 1 and 3 out to clean them off. I checked 5 and 7 because they were easy to get to and they were covered in soot. I cleaned them off right before I changed the o2 sensor.

Gas mileage shot up, power is back and the car runs way better. All this time I thought it was a knock sensor circuit based on the code that was coming up.

Man, was this thing a PITA to remove....