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running problem - stumble - unsteady idle - rich mix - blowing black smoke
1988 244 DL; B230F; LH-2.2; Manual 5-speed
I've spent 12 months working on a running problem to have gotten to a, apprehensive, conclusion.
It may date back to March 2011 when I failed emissions - which I did pass with flying colors. I had similar stumbling symptoms after my first attempt to adjust the idle (ultimately resulting in replacing the AIC). After numerous repairs (see: http://www.brickboard.com/RWD/volvo/1481789/220/240/260/280/recap_emissions_failure_repairs_iac_idle_rpm_mpg_pcv.html)
I may have only masked the problem until March 2012 when the symptoms started intermittently and then decided to move in semi-permanently. I say semi-permanently because the car did not have the symptoms 100% of the time but when it did they were getting worse.
It started as an intermittent hesitation and rough idle.
I went through at least 2 tanks of gas before the problem started showing up in dropping MPG.
MPG dropped from 22 down to 12 in three tanks of gas. I stopped using the car after two declining MPG records of 17 to 16 MPG. The 12 MPG reading was when I did a 1/2 tank fill-up with fuel injector cleaner.
The nature of the symptoms had me thinking the problem was electrical.
The engine was running rich - obvious from the drop in MPG. At the end there was black exhaust when revving the engine while in Park.
Prior to this problem the engine fired on first turn of starter. During the problem it took about 3 turns.
I went through many operations to get to a "repair" - normally running car.
-Phase 1-
Checked:
Air filter and preheat door - clean and still wedged shut
Vacuum lines - no leaks
Fuel system grounds and all others I can find - replaced AC to block ground that had been broken.
Fuel Pumps - both heard operating
Injectors - resistance at ECU is good - all are clicking
Battery - 12.2 volt
Coil - in spec
"midnight test" - no sparking
AMM - resistance at ECU is good (did not check burn off)
IAC - resistance at ECU is good
Temp Sensor - 18 months old - resistance at ECU is good
Cooling Thermostat - in good order
Replaced:
-Original Fuel Pressure Regulator replaced with new Bosch unit ($40 for fuel line pressure test ... $60 for new FPR)
-spark plugs - plugs were coated with dry black (carbon) from running rich.
-1 year old oxygen sensor was coated with (carbon) from rich running swapped w/ old original O2 sensor from 2011.
The replacements eliminated the majority of the stumbling though the idle was still uneven.
The idle dropped almost to stalling (dash lights come on) before recovering when taking my foot off the throttle.
-Phase 2-
Adjusted Throttle (stop, TPS, link):
The dropping idle was gone and idle was recovering "normally".
The car was not hesitating and had power though something "felt" off. It was slight and I can not describe it in more detail.
The idle loped when cold. It was more stable once the engine warmed up. But oddly jumped intermittently to a higher RPM (revved) briefly then settled down again.
There was still exhaust visible while driving at night (seen in other's headlights) and when starting from a stop or accelerating. There is still black smoke seen at the tail pipe when revving the engine while in park. The exhaust smells a bit like burning plastic when running - I assumed that was unburned fuel.
Check:
Timing - the mark is not stable but vibrating around 12 degrees (+/-) 2 degrees - which is spec.
-Phase 3-
Replace existing AMM w/ used of same # (may have had the CO screw tampered with):
No more running symptoms. Idle is high and does not drop when engine warms up.
-Phase 4-
Adjusted Throttle (stop, TPS, link) again:
The idle is way higher (2000 (?) RPM) and the car will drive in first gear without using the gas. I have a manual transmission.
The idle does drop to "normal" when I take my foot off the throttle but recovers to a high 2000 (?) RPM.
Test drove to salvage yard.
I swapped in a 3rd AMM with no noticeable difference in idle.
I swapped in the original AMM and the exhaust became obviously worse and the old stink was back.
I swapped back to the 2nd AMM from Phase 3 and the exhaust cleaned up.
I purchased a used Throttle body with TPS attached.
-Phase 5-
Replace:
Cleaned salvaged Throttle Body (TB) and TPS and installed using original adjusted throttle link.
-eureka (?)-
Car starts and idles evenly though high. Drives normally.
I adjusted the idle down by ear using the Throttle Body idle adjusting knob, until I can get access to a desk top tack.
-Phase 6 - follow-up maintenance
Replaced oil due to excess gas in combustion chambers getting into oil system. The oil was obviously thinned out at this point.
After the fact ... thinned oil will grind up your engine if you keep driving it. Invest in some cheap oil filters and oil and change it when you can smell gas on the dip stick ... or sooner - though I do not have a symptom to check for.
16.97 MPG at first fill-up after major improvement.
20.3 MPG on first half of next tank of gas.
Check/Adjust idle:
Disabling IAC by grounding from B/W connector wire, minute reduction in idle. Tach shows 800RPM (+/-). After closing Throttle Idle Air Control Knob all the way down idle is only reduced to 780 RPM (+/-).
Timing mark is still at 12 degrees (+/- 2).
-Phase 7 - high idle
Check plugs:
Pull #1 plug. Carbon has been cleaned off insulator, ground and central electrodes by Gumout Concentrated Fuel Injector Cleaner. Check all plugs terminal nuts are tight and plug is tight in socket.
Check Throttle Plate:
fully closed
Check IAC/Vacuum leaks:
Block air path to IAC. Car will start and idle though obviously at a low and unsteady rate. Found loose pipe clamp on the intake side of the IAC and tightened it.
Replace: Oil Filler Cap gasket. New gasket is much more flexible than old gasket.
Check major air paths by blocking at IAC (coming and going), Charcoal Canister (EVAP) large hose, Oil Vapor Trap Inlet with sandwich bags.
*All blocked - Car will start but not hold idle.
*Open IAC outlet to throttle body - will start but not hold idle.
*Open Charcoal Canister - will not start.
*Open IAC inlet - will start and hold idle.
*Open Oil Vapor Trap inlet - still running.
Idle does not sound lower.
20.26 mpg
Check/Adjust Idle: Very little reduction in RPM when IAC is grounded. Was able to close Idle Air Control Knob a little more and lower RPM a bit but it still is high 750+.
water injection clean engine:
Warm engine.
Run 1 cup distilled water through engine by vacuum hose connected to EVAP small orifice nipple in front of throttle plate.
Drive car.
Repeat w/ another cup of distilled water and drive till tail pipe is dry.
-Engine may sound smoother.
replace:
Swap original (first) Oxygen Sensor installed while working on stumble with (second) O2 sensor from emissions work in 2011.
Engine may start more readily and sure seems quieter and smoother.
21.16 mpg
Mileage is still not all the way back 22 +/- mpg. So I am moving this to a High Idle problem.
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1988 244 DL; B230F; LH-2.2; Manual 5-speed
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