Cold Start Idle Fluctuation 2001 V70 T5

[Noie]

Hello everyone,

I'm not trying to spam the forum, but my Volvo intermittently has cold start RPM fluctuations. Attached below are videos from 3 different cold starts. The video labeled Cold Start 3-1 is the most severe I've filmed (Notice the instrument cluster light fluctuation as well). Weather/Temperature does not seem to factor into it. It occurs on about ~60% of starts I would say to varying degrees of severity. One of the starts attached below it fluctuated quite a bit. I have not had it stall out, and it always evens out at about 1000 rpm after 5 to 20 seconds. It never occurs on hot starts, must be sitting cold for at least 8-10 hours.

Some things I know:

- It started up in the winter sometime after I had the timing belt replaced and associated service done. I did not notice it to be directly caused by the timing belt service.

- I had a MAF issue a couple years ago and replaced it then so it is not a particularly old unit. That was about 25k miles ago. I've heard Bosch units are pretty poor quality though.

- My battery tests fine but is quite old (2017). I've read this can possibly cause fluctuation since the alternator needs to pick up the slack.

- I tried a tank of premium 91 octane fuel (versus the usual 87 octane) and it the issue went away. It started smooth every morning.

To conclude, I think it may be the MAF, old battery, idler tensioner not set correctly, or a vacuum leak. I'd appreciate any input you all may have.

Thanks, Noah.

[jonesg]

so you found hi test eliminates the problem but conclude the problem to be something else?
What about a litte bottle of dry gas octane booster and don't allow the tank to run low.
What is the CEL , read any codes?

[abscate]

The 2001 uses the VVT to inject more cold air to burn off the excess start fuel. You should have a high idle for 15-20 seconds, maybe with some rough running? I can’t watch the movies on iPad to tell

[Vova585]

You have a car with 265k on it..everything is worn inside. Also the engine is designed to run on premium fuel and not 87 or 89. The more wear on your engine, the harder it is for the system to balance it especially with low octane fuel. If the fuel grade fixed your issues- amazing, dont complicat it. Put non ethanol fuel in it(it served you 265k, it earned it) and a bottle of fuel injector cleaner every month(royal purple is my "drug" if choice).
Then look into check engine light and see what it needs.

[volvolugnut]

My 2001 V70 T5 (220K miles) also has a occasional rough cold start like yours. It always smooths out after less than a minute so I try not to worry about it. Mine might have dirty injectors that a likely originals. I also run low octane fuel because higher octane is hard to find here without ethanol.
volvolugnut

[DavidE7]

I was having slightly rough idle on my turbo Volvos and I already did all the usual stuff:
-New spark plugs with verified gap
-Good spark plug coils
-Clean throttle body
-Clean PCV system
-No leaks in the intake system after the mass airflow sensor
-Cleaned the MAF hot wire with spray MAF cleaner
All my cars have high mileage so I decided to try ultrasonic fuel injector cleaning and balance verification from this company in Ohio:
https://www.injectorexperts.com/product ... h-services
The pre-cleaning report showed that the 5 injectors weren't squirting the same volume of fuel. Each of the Volvos ran smoother at idle with the ultrasonic cleaned injectors installed. Unfortunately, I don't have a way to measure the improvement in idle smoothness.

I tried finding any references in VIDA to engine adaptation for balancing the injectors. The engine performance data lists a single injector open/squirt time for all 5 injectors when viewing live data when the engine is running. I couldn't find where the engine control computer is checking very high speed oxygen sensor changes for the exhaust bursts from each of the 5 cylinders and correcting the injection time to tune each injector to deliver the exact same volume of fuel. Getting the injectors cleaned and verified to squirt the same amount of fuel should improve idle quality and fuel economy. I haven't seen a noticeable improvement in fuel economy. The 5 spark plug electrodes all look the exact same after I installed the clean injectors and drove a thousand miles.

[Noie]

It turns out it was an un-cleared ECM-644A code. I had replaced the VVT exhaust solenoid, had the t-belt done, and cam seals done back in the fall/winter. With the reset of the code 3 days ago, the vehicle has a normal cold start. This includes the initial rev to ~1500rpm before returning to stabilized idle. My symptom before was there was no initial 1500rpm rev. The car would just go right to 900rpm idle and stutter for a bit before stabilizing.

[jonesg]

interesting. I wondered what difference a hard set code makes,
the ECM turned off a function.
Then required it be notified after the repair is made in order for the ECM to reactivate the particular function again.

[abscate]

The VVT code disables vvvt and sets advance to 0 degrees until cleared. I believe that code requires a hard reset , since it stops monitoring cam flank angle once set