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Cold idle stumble

LIVEAnimals

LIVEAnimals

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For the last couple months or so my 90 v2500 Sub has been having some cold idle stumble issues. As stated the stumble is only if the rig has been sitting long enough and is stone cold. Tonight I let it warm up until it kicked off high idle and you could hear it clear up. If I put it in gear before then it stumbles. In the last two months its had new E3 plugs and MSD wires, new fuel filter, and had a K&N filter about a year ago. It also got a 180° Tstat about 3 months ago
 
Sounds like maybe a coolant temp sensor starting to go bad. If you check that out or get a new one, make sure it's the two wire sensor(green and black wires) located either on the intake manifold or t-stat housing, since this is the one that sends a signal to the ecm. There is another sensor on the driver's side of the engine that is only for your temp gauge.
 
Put the 195 thermastat back in.

Is the hot air tube still hooked up?

Put AC delco spark plugs back in.
 
X3. The lower degree thermostat is not good for newer engines. 195 helps it burn better with efi. The Delhi plugs really are the best. I've used accel with great success as well. I tried using the platinum plugs once and my engine ran worse.
 
If they are Delco replacement plugs for the application then copper, platinum or Iridiam should be the same. Just cost more and last longer.
 
eagle mark said:
Put the 195 thermastat back in.

Is the hot air tube still hooked up?

Put AC delco spark plugs back in.
Click to expand...

Everything is still hooked up

ryoken said:
I refrained from saying it, but... x 2..... ;)
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chulisohombre said:
X3. The lower degree thermostat is not good for newer engines. 195 helps it burn better with efi. The Delhi plugs really are the best. I've used accel with great success as well. I tried using the platinum plugs once and my engine ran worse.
Click to expand...

I can understand the Tstat problem if the problem was still there when warmed up but it's not. The problem is when the temp gauge isn't even registering a temp so how would a 195° fix it, it runs great when it gets to 180°. I have always ran 180° tstats without a problem.
 
I had a similar problem in my '91 K5. It turned out to be the coolant temp sensor, which was removed by the PO during an engine swap and never replaced. There were a couple other issues affecting idle even when warm, but simply installing a CTS made a huge difference on cold starts. Just my $.02, hopefully it helps.
 
LIVEAnimals said:
I can understand the Tstat problem if the problem was still there when warmed up but it's not. The problem is when the temp gauge isn't even registering a temp so how would a 195° fix it, it runs great when it gets to 180°. I have always ran 180° tstats without a problem.
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Your never warmed up. I guarentee better fuel milage if T stat goes back to what's called for and what ECM thinks is warmed up.

Second guess cause I'm not there and going by what you tell us is the spark plugs. Snake oil plugs have caused more issues then you could ever imagine. You'll never find a spark plug to make that engine run better then OE.

After that could be lots of mechanical things showing age like distributor, cap, rotor, have you changed to a non GM EST in distributor, what's the fuel pressure, is there any vacuum leaks, throttle shaft wear cause throttle blades to close which is horrible for fuel and air atomization.

Check the heat riser to make sure it is letting heat from exhaust manifold in when cold. These are very reliable excellent unit but do fail.
 
eagle mark said:
Your never warmed up. I guarentee better fuel milage if T stat goes back to what's called for and what ECM thinks is warmed up.

Second guess cause I'm not there and going by what you tell us is the spark plugs. Snake oil plugs have caused more issues then you could ever imagine. You'll never find a spark plug to make that engine run better then OE.

After that could be lots of mechanical things showing age like distributor, cap, rotor, have you changed to a non GM EST in distributor, what's the fuel pressure, is there any vacuum leaks, throttle shaft wear cause throttle blades to close which is horrible for fuel and air atomization.

Check the heat riser to make sure it is letting heat from exhaust manifold in when cold. These are very reliable excellent unit but do fail.
Click to expand...

Gas mileage won't change the slightest with a 195° trust me, everything I've tried still only yields 10mpg. It could probably benefit from a cap n rotor. I'll check the heat riser and possibly throw a temp sensor at it.
 
we wheren't saying your issue was the t-stat, or plugs, just the vehicle is better off as we suggested... TBI likes 195 better, fact... it helps the system go to closed loop... which WILL affect mpg, among other things, plug life, etc...

speaking of, the fancy plugs will perform no better than oldschool AC Delco's, and sometimes worse.. try throwing Boschs in a chevy and see how they do...

as to your problem, first thing to do would be to pull codes...
 
My 90 2wd 5.7L Auto Suburban get's 14 worst case, 18+ highway... 16 is an average figure.

You can check Coolant Temp Sensor in data or by OHMs. If failed it will cause horrible gas milage because the ECM thinks its -40C outside all the time. But you would have worse issues then you do now.

Do you have headers?

Wish I could help more...
 
eagle mark said:
My 90 2wd 5.7L Auto Suburban get's 14 worst case, 18+ highway... 16 is an average figure.

You can check Coolant Temp Sensor in data or by OHMs. If failed it will cause horrible gas milage because the ECM thinks its -40C outside all the time. But you would have worse issues then you do now.

Do you have headers?

Wish I could help more...
Click to expand...

No headers, completely stock besides the K&N
 
Mine hits closed loop no problem with a 180 degree thermostat. I run factory 2002 454 plugs in mine, which are factory platinum AC Delcos. But I HIGHLY doubt them E3s are the problem as far as plugs go, they are a very good plug, just to much $ for my blood.

Something to check is not necessarily the heat riser, all it is is a tube that connects to a heat manifold around the manifold to the intake itself. But check the flapper door thingy, it uses a wax filled dealy that opens a flapper door when it warms up and sucks cold air out instead of warmed air. See if it is rusted shut and preventing cool air from entering the TB.

Vacuum leaks could be a problem as well, use brake clean all around the intake and such and try and tighten the the TB down and see if it helps.
 
454Sub said:
Mine hits closed loop no problem with a 180 degree thermostat. I run factory 2002 454 plugs in mine, which are factory platinum AC Delcos. But I HIGHLY doubt them E3s are the problem as far as plugs go, they are a very good plug, just to much $ for my blood.

Something to check is not necessarily the heat riser, all it is is a tube that connects to a heat manifold around the manifold to the intake itself. But check the flapper door thingy, it uses a wax filled dealy that opens a flapper door when it warms up and sucks cold air out instead of warmed air. See if it is rusted shut and preventing cool air from entering the TB.

Vacuum leaks could be a problem as well, use brake clean all around the intake and such and try and tighten the the TB down and see if it helps.
Click to expand...

Good stuff, I'll check that
 
If you can get it to run long enough to throw a code for a bad CTS, it will still run when warm. It must set the ECM to a "failsafe" temp, but it will run very rich when cold. Mine did this until I reset the code before I installed the sensor, afterwards it was dumping fuel like crazy and flooding. If there is no code I doubt the CTS is completely bad. If it is the CTS at all, I would guess it is just reading inaccurately, possible from being dirty or just old and wearing out, though it's not a moving part, and seems pretty sturdy.
 
ljense8 said:
If you can get it to run long enough to throw a code for a bad CTS, it will still run when warm. It must set the ECM to a "failsafe" temp, but it will run very rich when cold. Mine did this until I reset the code before I installed the sensor, afterwards it was dumping fuel like crazy and flooding. If there is no code I doubt the CTS is completely bad. If it is the CTS at all, I would guess it is just reading inaccurately, possible from being dirty or just old and wearing out, though it's not a moving part, and seems pretty sturdy.
Click to expand...

If it throws a code the CEL will come on right, there is no CEL and its not running rich just a choppy idle.
 
replace the cts,its easy and cheap,13 dollars at carquest,then go from there,only takes 5 minutes to swap out
 
LIVEAnimals said:
If it throws a code the CEL will come on right, there is no CEL and its not running rich just a choppy idle.
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Correct, the CEL will come on and when scanned will read code #15. This is why I'm not sure if it would be the CTS, and if it was the CTS, then not a complete failure, just inaccurate reading. These other guys that have been commenting seem like they know a lot more than I do, this is just one of the things I have dealt with. The other thing to check is fuel pressure. From the factory anywhere from 9-12psi was acceptable(mine clocked in at about 8 before I bumped it up), but it really needs about 12-13psi, especially if you have anything done performance-wise. If you already have good fuel pressure and a good CTS, then I would go with what the other guys can recommend, since I don't have enough experience with these engines to be much more help.
 
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