m20b25 hard to start cold

[funcrew]

My bone stock m20b25 with 90K on it is very hard to start cold, but runs strong and smooth even before the coolant warms up. It cranks strong, but takes a long time to fire when the temperature is below about 45F. Idles rough for maybe 10 seconds, then smooths out. Starts right up when warm. Gas mileage is fine and it passes smog.

Recent maintenance includes:

new VDO fuel pump
spark plugs, rotor, distributor cap
rebuilt and flow tested injectors
oxygen sensor
EDIT: replaced both coolant temperature sensors (to cluster & DME)

The ICV moves freely and the idle is steady.
Smoke test was done recently and all vacuum leaks were fixed.

Instead of paying my corner mechanic a couple hundred bucks to diagnose this thing, I'd rather throw that value of parts at it. What would you try next, and in what order, or what DIY diagnostic would I do at this point?

[MR 325]

These are the things I would consider:

Coolant temp sensor to ECU
TPS needs to be adjusted or replaced
Bad fuel pressure regulator

Those things should also cause a decrease in gas mileage though...

[funcrew]

These are the things I would consider:

Coolant temp sensor to ECU (OP: Done - forgot to mention that)
TPS needs to be adjusted or replaced
Bad fuel pressure regulator

Those things should also cause a decrease in gas mileage though...

Thanks Matt. Are there a good write-ups on testing the TPS and FPR?

[paperplane94]

Thanks Matt. Are there a good write-ups on testing the TPS and FPR?

The Bentley manual :)

[funcrew]

The Bentley manual :)

How about that? Turns out there's a cold-start troubleshooting guide on page 3-14. Just ordered a fuel pressure kit from Harbor Freight.

Thanks