Volvo Maintenance Hints for 7xx/9xx - Bill Garland's Nuclear ...

has to be done in sequence.
Ran a can of BG44K through the tank to clean up intake valve and fuel
system deposits.
Car now runs very strong.
Poor Idle: Injectors Need Cleaning. See Injector Cleaning for more information on
how to solve chronic idle problems due to dirty injectors.
Poor Cold Idle: B230F/T ECU E-Prom Needs Update. [Inquiry] My wife's 95 945T
(90k miles) starts fine on a cold (below 40F) start, but idles like crap for 20 to 30
seconds. If I hold my foot on the gas and keep it at 1500 rpm for 8 to 10 seconds, its
fine. Car idles nicely when warm, and runs like a dream. When I pull the plugs, they
look great. I've replaced ECT and other parts and cleaned the TB. [Response: Abe
Crombie] Go to a dealer and have them look at Volvo Service Bulletin 28-102
"modified e-prom for cold start with low rvp fuel". This says the symptoms are: car
starts and then immediately dies and requires re-start. Runs rough for the first 45
seconds and may hesitate on acceleration. Recent EPA regulations have
necessitated changes in the formulations of gasolines (i.e. "oxygenated fuels"). The
result of these reformulations has been a decrease in the relative vapor pressures
(volatilities) of these fuels, which seems to be particularly problematic for cold starts/
idling. The updated eprom chip to be installed in the ECU is the fix to make it have
correct fuel mixture computations for cold start. You must have the number from your
ECU in order to cross-reference the correct eprom update kit P/N. The change
procedure described in 28-102 requires careful attention to static discharge.
Idle Speed Control Problems.
High or Unstable Idle. [Symptom] My 945T (94 - 99k) has been having high/low idle
problems - it wanted to idle around 400 or 1500+ - there was no middle ground.
[Solution] Replace the throttle position switch, which detects idle when the switch is
closed and, if faulty, will cause idle problems.
Idle Speed Control on Late 7xx/9xx. In Volvo 700/900 cars with LH2.4 fuel injection,
the idle speed is controlled by a bypass system. When your foot is off the gas, the
throttle plate is fully closed and a separate idle air control valve admits the required
amount of air to get the engine to idle at 750 rpm. This separate valve is controlled by
the computer. No adjustments are possible.