1999 V70T5M56 Poor cold idle troubleshooting Topic is solved

[abscate]

Brief descriptor of problem
With temperatures below 35F (2C) the engine runs on 4 cylinders with a consistent miss. After about 2-3 minutes of idle, all 5 cylinders come in smoothly. Car runs at partial load on all cylinders but idles on 4 during cold period. After warmup and hot start no missing, engine smooth and powerful.

P0300 will set about 1/2 the operating cycles, occasionally pointing to P0304 and P0305

Items to be evaluated

Cold compression in all 5 cylinders
Spark Plugs and condition
Fuel injectors and condition
ECT resistance

[RickHaleParker]

occasionally pointing to P0304 and P0305

Misfire on adjacent cylinders can be caused by leakage between the cylinders.

My best theory at this point is, the you have a marginal head gasket leak between cylinders 4 and 5 that seals up when the head expands due to heat. Two compression tests, one done when the engine is stone cold, the other done when the engine is at operating temperature might produce data that supports this theory. If you try this, get data from all 5 cylinders on both the cold and hot test.

[erikv11]

Cheap and easy to add to the list of items to evaluate (and worth adding):

Get some starting fluid on the edges of the intake manifold where it meets the head, especially near 4 and 5.

Oh and remember, you can swap injectors around when traveling down that path.

[abscate]

Possible head gasket but this is a HPT. I don't think it's going to fix itself under boost.

I left valve stems off the list, too

[abscate]

I'm getting the P0304/5 about 20% of the time and always together. I'm not putting a lot of stock in those as rough running will fool the ECU trying to locate missing cylinders

Added checking torque on intake manifold bolts to list

[RickHaleParker]

Possible head gasket but this is a HPT. I don't think it's going to fix itself under boost.

On a HPT, boost does not come on until about 3000 RPMs.

[abscate]

Yeah but a cylinder head leak isn’t going to fix itself on a HPT. Possible but a sparse bet.

...and this morning , start and idle was smooth as silk at 20 F so points s more to a faulty component than major mechanical

[abscate]

Cold compression test was low to spec, but spec is warm

I showed 125-135 psi across all cylinders, spec is..



NOTE: Measure compression with the engine hot and at wide open throttle

Normal value B5234T and B5254T: 1.1-1.3 MPa (156-185 psi)
Maximum deviation between cylinders: 0.2 MPa (28.4 psi)
NOTE: This applies when the engine is warm and the throttle fully open and the engine being turned by the starter motor at 4.2-5.0 rps (250-300 rpm).

[abscate]

Hmmm- a bit more data on the mix. This car has always run at 87C, but on the highway, the AUTEL recorded 83C.

The thermostat is a Wahler - about one year old. This could be a point to a failing ECT.

[erikv11]

Well, get those resistance values, man!

And/or swap in a spare.