94 Volvo 850-high idle after driving

[Volvofan94]

Hi Everyone!

Been going through the rest of my mechanical things to fix on my 94 Turbo 854 as summer winds down. I was hoping something else I fixed earlier would have taken care of this question I have with the car.

After about 30 minutes or so of driving, I put the car in Park, the idle climbs to about 1200 RPM. The car does this when it is either in Neutral or Park after driving. When I have the gear selector in Drive the idle is normal at about 900 RPM. When first starting the engine in the morning, idle is fine as well. The CEL isn't on and other than this the car runs and drives excellent.

A list of the few things I have replaced/cleaned:
1. Cleaned the throttle body, MAF, and Idle Air Controller
2. New Sparkplugs
3. New Fuel Filter
4. Replaced the throttle cable and verified there wasn't any obstructions on the outside or inside of the throttle body.

A couple of questions:
Could there be something I may have missed or should be cleaned to see if it will correct the issue? Is it normal for the Turbo engines to have a higher idle when warm vs. cold compared to the non-turbo engines?

Thanks!
-Volvofan94

[jblackburn]

Idle is usually 100 RPM higher in park than drive, but never 1200.

Is the temp gauge always pointed at the 3:00 position once the car is warmed up? Kinda sounds like the computer thinks it's too cold.

[Volvofan94]

Hi jblackburn, yes, the temp gauge is at 3:00 when the car is all warmed up.

Funny you should mention the computer; I am running the 628 T-5R ECU in my Volvo.

I haven't tried to swap the factory ECU back into the car after purchasing the T-5R ECU. I wouldn't think the higher performance ECU would be causing the problem, would it?

Thanks!
-volvofan94

[Volvofan94]

A quick update to my previous post...I swapped the 628 T-5R ECU for my factory one and took the car for a drive for about 30 minutes. Same symptoms as with the 628 when I put the car in park.

I'm guessing there may be an issue with my coolant temp sensor sending incorrect readings to the ECU when the engine is warm? I can check the resistance with the engine warm and temp gauge at the 3:00 position and post back my findings.

[Volvofan94]

One more update: The issue has been resolved!!

Turns out my EVAP system was broken and needed to be replaced. Figured the EVAP Purge Valve was the culprit after I tried to go into the upper rev band and not two minutes later the CEL came on and there were many CEL codes stored. One of them being error code 315 for the EVAP purge valve. I thought I would start by replacing the Purge Valve and deal with the other codes later on (if they came back).

My car (as with most 94 Volvo 850 turbos probably) has a rubber canister on the driver's side of the fan shroud under the fresh air intake pipe. I thought this whole unit needed to be replaced (I bought an OEM Evap Purge Valve replacement kit online). As I continued to work I figured out the case actually splits in half and inside is the Purge Valve and its extension wire to that plugs into the rest of the car's ECU. Below is what the old Purge Valve (red arrow) looked like after the case was removed.

Old Evap Purge Valve. Rubber case removed. Extension cable removed.

Old Purge Valve.jpg (45.05 KiB) Viewed 1278 times

Below are the case parts:

The case and extension wire.

Steps to repair:
1. Remove the throttle body cover, fresh air intake hose, and the upper solid turbo intake pipe (I removed these parts for better access to the Purge valve).
2. Remove the two screws that hold the protective case to the fan shroud. This is found on the driver's side of the car below the fresh air intake. Unplug the electrical connector.
3. Remove the upper and lower hose clamps on the rubber protective case.
4. Bend the holding bracket enough to release it from the rubber case. Over the years the heat semi fused the rubber to the metal as I removed the metal holding band. Just be careful as to not tear the rubber casing. After the metal band is removed, the rubber case just splits in half to reveal the EVAP Purge Valve. Don't throw the case away as it will be needed for reassembly later.
5. Remove the vacuum line from the intake manifold and the lower end of the EVAP Purge Valve.
6. Remove the old Purge Valve from the vehicle.
7. Installation is in reverse of removal steps.

All in all it's a pretty easy fix and it feels good to have my car working again. It sure made a difference in power and hopefully fuel economy.

Good luck!