1997 850 - Idle Stutters When Warmed Up

[Colt99]

So as the subject says, my idle is just fine when it's cold, but as it warms up to operating temperature, it starts stuttering really badly.

The first time this happened, it stuttered for a few minutes, then I gave it some gas and it ended up stalling. After it cooled down for 20-30 minutes, it started back up with no problem. It didn't stutter until it heated up once again.

I've replaced my MAF Sensor, Flame Trap, Fuel Injection Idle Air Control Valve, Fuel Pump Relay, Air Filter, Throttle Control Pulley System, and reconnected the air hose from the grill to the air filter housing, as I saw it was popped off.

I've no clue what it could be, as this is my first car and I want to ask here before spending money unnecessarily.

Thanks!

[scot850]

I would check the fuel pressure at the rail. When was your fuel filter last replaced?

I would also give any vacuum hoses in the engine bay a good check over for splits.

I'd also check the coolant temp sensor connector and the wiring at the connector for corrosion and check it's resistance values.

Finally, check the injector relay on above the radiator for cracked, rusted or broken wires.

Neil.

[Colt99]

Hey there. I finished replacing the fuel filter quite literally this morning, hoping it'd fix it, though unfortunately not.

I ordered a new temp sensor, and a new thermometer, so I'll be replacing both of those sometime this coming week.

I'll check over everything you noted, thanks a lot for your help, I appreciate it.

[matthew1]

Does the dash dim/flicker also? If so, check ground strap, battery cables, battery (age).

[erikv11]

Check under the distributor cap for any of these common issues that get worse as the engine warms up:

- a blown rear cam seal leads to accumulated oil and/or moisture
- worn rotor contacts
- worn contacts on the cap

[matthew1]

^ Yes, that too.

A good 20% of these air/fuel-presenting symptoms are spark.