High Idle when car has been running for a while Topic is solved

[lcc014]

Volvo 850 modules and Flash codes. Smoke injection is the best leak detector. You can use starting fluid on the intake side of a running engine for leak detection. When a leak sucks in starting fluid you will hear the engine surge.

Could you provide more detail on how to use the starting fluid on the intake side of 850 ? Do I need to disconnect any hose while engine is running to inject or spray the starting fluid ?

Thanks,

Ching-Ho Cheng

[misha]

Yes...but that setup is pretty rare for '95.
Usually...they are Jetronic.

[lcc014]

Yes...but that setup is pretty rare for '95.
Usually...they are Jetronic.

Okay, got it, thank you.

Ching-Ho Cheng

[RickHaleParker]

Could you provide more detail on how to use the starting fluid on the intake side of 850 ? Do I need to disconnect any hose while engine is running to inject or spray the starting fluid ?

Start the engine. Spray around the intake side. If you hear a surge you located a leak.

[lcc014]

Could you provide more detail on how to use the starting fluid on the intake side of 850 ? Do I need to disconnect any hose while engine is running to inject or spray the starting fluid ?

Start the engine. Spray around the intake side. If you hear a surge you located a leak.

Thank you. I will give it a try.

Ching-Ho Cheng

[lcc014]

After trying to check for vacuum leak by spraying carb.cleaner around the intake manifold, vacuum tree, throttle body, big air hose between airbox and throttle body. The result was no leak. Then I replaced the thermostat (there was a minor leak of coolant around the upper thermostat "cover" and the coolant temperature sensor. These 2 parts were about 12 years (200k miles) old. Connector of the coolant temperature sensor was so bristle that I had to get a new connector from dealer and 2 new terminal wires from Dave's Volvo page. After changed out these 2 parts, I test drove the car today and problem still existed!

After I parked my car back to driveway with engine still running, idle speed was about 1500 RPM. I looked at the throttle body from above and here was what I found:

There was a gap between the throttle stopper and the "throttle control pin" (I don't know how to call this). When I used my hand to grep the throttle cable wheel and turned it clockwise.

The gap was closed and I heard the engine speed back down to normal sound. I checked the engine rpm in dashboard, it was back down to about 850 rpm. So the root cause is either the binding throttle body valve/flap spring or the control rod between the throttle body wheel and the valve spring.

Any suggestion to unbind this throttle body valve control spring or the control rod so that when I let go of gas pedal, it would return all the way and hit the stopper without any gap ?

Thanks,

Ching-Ho Cheng

[abscate]

That linkage looks pretty crusty and rusty, can it be removed and cleaned up?

[lcc014]

That linkage looks pretty crusty and rusty, can it be removed and cleaned up?

Any idea to remove it without breaking the metal ball within the linkage ends ?

[lcc014]

This morning, I used my RC helicopter tool - ball link pliers to undo the throttle control linkage (pulley end).

Once that end was out, the other linkage end came off easy.

I cleaned up the linkage and the two "balls" on the pulley and throttle body spring. I also sprayed so much carb. cleaner to the throttle body spring and the throttle body valve shaft (both ends of the shaft) to try to clean up any grease on them. I then applied grease on the linkage end so that the linkage went back into the balls easier and very easy to be moved the hand. I will test the car tomorrow.

Thanks,

Ching-Ho Cheng

[lcc014]

Test drove the car today and problem still there when car is engine bay was warm/hot. I could see the gap between the throttle spring and the stopper. I shut down the car and removed the throttle cable from the pulley, the gap immediately closed by the throttle plate spring. So the issue most likely to be the throttle cable itself. With the throttle cable attached to throttle pulley and engine is hot when I stepped on the gas pedal a little bit to rev. up to pass 2k rpm, then let go the gas pedal, I could see the throttle valve spring did not touch the stopper - gap. The gap was quite wide that engine rpm went up to about 2k at idle. I manually turned the throttle pulley clockwise to close the gap and idle back to about 850 rpm. So it looked like throttle cable was the one to hold the throttle spring not touching the stopper and created high idle speed. When I shut off the car for a hour or so, I checked the gap and it was gone.

My question about the electrical connector on the throttle cable. What is that electrical connector for ?

I will replace the throttle cable, this part was the original since 1995.

Thanks,

Ching-Ho Cheng