Surging during warm-up then random misfire at idle.

[Georgeb]

So I have a problem I see others have had but perhaps not quite the same. I also noticed there aren't many posts describing the "fix". If this is covered somewhere feel free to point me in the correct direction. The offender is my 87 Sierra R3500, 5.7 TBI, SM465. When I start it cold it runs fine in open loop but as it warms up it develops an idle surge that lasts until it reaches near full temp and then the surge goes away and is replaced by a random misfire at idle.
I have done the following:
-Checked for vacuum leaks with carb cleaner and replaced the plastic MAP and PCV lines. They weren't leaking but I didn't trust them.
-Cleaned all the grounds and checked all the connectors.
-New AC Delco plugs, wires, cap and rotor.
-New fuel filter.
-New AC Delco CTS
-Inspected and reset the IAC
-Checked the base timing. Currently at 4 DEG ADV.
-New O2 sensor (Bosch).
-New 195 DEG AC Delco thermostat.

Those were all parts that needed to be replaced and I don't want to just throw parts at it.

I am looking for a scan tool so I can see what the sensors are doing because I think that will help a lot and I was contemplating getting an ALDL cable and some software to log data.

The puzzling part is the Surge comes and goes with engine temperature.

I was wondering if it may be ignition related like the pickup coil, module or coil rather than MAP, O2, CTS, TPS related but I can't currently see whats really happening.

Does anybody have any insight or recommendations?

 

[Georgeb]

I also have this issue.

http://www.gmsquarebody.com/forum/showthread.php?t=12281

 

[Georgeb]

I also have this issue except the IAC isn't dragging in the bore.
http://www.gmsquarebody.com/forum/showthread.php?t=12281

My truck has auto cruise at 25 MPH but only in 4th gear. It will eventually slow down but it takes a bit. If I put it in third it will slow right down, I can hear the IAC whistle a bit while slowing in 3rd and once I get to too low of RPM it will buck like it is trying to compensate for the engine load or maintain he idle RPM again. I always thought it was normal because the MAP was sensing an engine load with a low throttle position. TBI is new to me. I have always been a Q-jet guy. I thought about going back to a Q-jet.....

 

[HotRodPC]

How about any codes? As dumb as it might sound, the VSS being bad can cause this problem you're talking about. The VSS communicates with the IAC. This is how the IAC actually knows the vehicle is actually idling or if it's off throttle coasting in gear. I"m not saying that's what's wrong for certain, but saying if it had any codes, pull'em and don't be surprised at what it can be. It can be something you wouldn't even think has anything to do with it, but it actually does.

So you're saying this is ONLY when the motor is cold? So it's very possible the problem is only when not in Closed Loop Operation. You've got the 195 degree tstat, you should have no issue getting to closed loop as far as temp goes, and probably not a temp sensor if it's for certain getting to closed loop.

 

[Georgeb]

How about any codes? As dumb as it might sound, the VSS being bad can cause this problem you're talking about. The VSS communicates with the IAC. This is how the IAC actually knows the vehicle is actually idling or if it's off throttle coasting in gear. I"m not saying that's what's wrong for certain, but saying if it had any codes, pull'em and don't be surprised at what it can be. It can be something you wouldn't even think has anything to do with it, but it actually does.

So you're saying this is ONLY when the motor is cold? So it's very possible the problem is only when not in Closed Loop Operation. You've got the 195 degree tstat, you should have no issue getting to closed loop as far as temp goes, and probably not a temp sensor if it's for certain getting to closed loop.

Sorry I forgot to mention I don't have any codes. I am not sure if I would say only when cold. Of the two problems I am seeing the first being the idle surging, it doesn't do it cold like right on start up or when its at temperature but right in between around the time the thermostat would be close to opening like it is going in and out of closed loop or something.

The second being the fast idle at slow speed I would expect when cold or in open loop but it also occurs when at temperature in closed loop. I was wondering about the VSS and will have to look into testing that somehow.

I think it's time to buy/make an ALDL cable and get some software. I was thinking about putting the ECM in diagnostic mode and trying to figure it the surging was happening in closed or open loop.

Any recommendations on software?

By the way, thanks for the reply! I like the site a lot and am glad I found it!

 

[HotRodPC]

I''ve not used any OBD 1 software at all. Some of the other guys like @Jims86 or @89Suburban, @foamypirate might know of some.

If there is no codes and having these issues, the EGR will need to be looked at too IIRC. Some of these other guys may have some better ideas too.

 

[Georgeb]

I''ve not used any OBD 1 software at all. Some of the other guys like @Jims86 or @89Suburban, @foamypirate might know of some.

If there is no codes and having these issues, the EGR will need to be looked at too IIRC. Some of these other guys may have some better ideas too.

IIRC? What does that acronym mean?

 

[foamypirate]

IIRC? What does that acronym mean?

IIRC means "If I Recall Correctly".

I use TunerProRT for my diagnostics. You can get the definition files from http://www.gearhead-efi.com.

You can find instructions on making a cheap diagnostic cable below (or order one from Robert if he still sells them). I followed these instructions and built my own cable and it works great:

http://www.gearhead-efi.com/Fuel-Injection/showthread.php?719-Uber-easy-DIY-USB-ALDL-Cable

 

[89Suburban]

Sorry I forgot to mention I don't have any codes. I am not sure if I would say only when cold. Of the two problems I am seeing the first being the idle surging, it doesn't do it cold like right on start up or when its at temperature but right in between around the time the thermostat would be close to opening like it is going in and out of closed loop or something.

The second being the fast idle at slow speed I would expect when cold or in open loop but it also occurs when at temperature in closed loop. I was wondering about the VSS and will have to look into testing that somehow.

I think it's time to buy/make an ALDL cable and get some software. I was thinking about putting the ECM in diagnostic mode and trying to figure it the surging was happening in closed or open loop.

Any recommendations on software?

By the way, thanks for the reply! I like the site a lot and am glad I found it!

I have that surging issue under the same conditions as you but it only happens once in a great while so I have been ignoring it. Try unplugging the vacuum line to the EGR valve and see if it stops.

Many times I have a high idle and have to put it in neutral in a certain sweet spot on the shifter for it to idle down and it will do so right away, like it is reading off the ignition switch or something. I have not had time to tinker with that but I just been used to throwing it in neutral to drop the idle and it's fine after that.

For instance, I will start the truck up cold at work, drive to my house across the street, hook my boat up, drive to the gas station about a mile away, shut the truck off. When I came back out and start it, engine is already warmed up but idles high, I drop it in neutral, it idles right down, and runs fine after that no matter how many stop and goes. Just a quirk that both my TBI Burbs have had and i just got used to it.

 

[Georgeb]

IIRC means "If I Recall Correctly".

I use TunerProRT for my diagnostics. You can get the definition files from http://www.gearhead-efi.com.

You can find instructions on making a cheap diagnostic cable below (or order one from Robert if he still sells them). I followed these instructions and built my own cable and it works great:

http://www.gearhead-efi.com/Fuel-Injection/showthread.php?719-Uber-easy-DIY-USB-ALDL-Cable

Like this:

 

[foamypirate]

Like this:

Yep, that's correct. The module gets power from the USB connection, so you just need ground and TX/RX to the ALDL port.

 

[Georgeb]

Forgive my ignorance but what will I use the definition files for? I am totally new at logging data. If this was a Q-jet it would be fixed already but learning new stuff is good!

 

[foamypirate]

Forgive my ignorance but what will I use the definition files for? I am totally new at logging data. If this was a Q-jet it would be fixed already but learning new stuff is good!

They are loaded into TunerPRoRT so it knows how to read the data coming from the ECM.

 

[Georgeb]

I should have known that! Will the free version of the software work for just the data logging/viewing I need to do?

 

[foamypirate]

I should have known that! Will the free version of the software work for just the data logging/viewing I need to do?

Yep, the free version works great for data logging and diagnostics views.