I’ve been trying to chase down an issue with my 1995 850 T-5R (109k miles) for a while, where the engine seems to randomly (and very frequently) “twitch” while idling. The twitches range in their intensity (steering wheel shakes mildly or very noticeably, and at no specific interval). It is especially noticeable in park and neutral; when in gear it’s still there but not as noticeable.
At idle, ignition timing advance @ cylinder 1 randomly fluctuates between 3 through 9.
I only use 91 octane fuel.
I change the oil every 3k miles and only use Mobil 1 High Mileage full synthetic.
Also, RPMs dip by about 100 when doing a “rolling idle” (no brakes, just letting car roll @ idle) but go back up to the normal 840 when at a complete stop. This also happens when coming to a stop as the car enters idle, until completely stopped via brakes when it goes back up to 840 again. Here are some more of the symptoms:
- RPM appears mostly unaffected by the twitch, but occasionally dips from 840 down to 800 (live readout using OBDII scanner) and right back up to 840 when idling in park or while stopped in drive.
- Exhaust smells pretty bad, like the engine’s running rich.
- Aside from the frequent “twitching”, the car has a slight roughness or vibration when slowly accelerating (very minimal throttle) from a stop, until around 1,200-1,500 RPM and above, where it seems to smooth out. I've replaced both front axles and wheel hubs/bearings in the last 3k miles, but that didn't fix it.
- My MPG averages 20-22 combined according to trip computer. I drive roughly 50/50 street and highway.
Here’s a list of everything I’ve attempted so far trying to remedy the issue (all parts used are Genuine/OEM unless otherwise noted)
- Replaced motor mounts – ALL of them (including tranny torque mount and firewall mount). Upper engine and firewall mount are IPD poly.
- TUNE UP - Plugs , plug wires, distributor cap and rotor @ 93k miles. I first replaced them shortly after buying the car (@ 92k miles) because it had a pretty hefty misfire that was easily felt, and doing so eliminated the noticeable misfire.
- Had to replace plugs, dist. cap and rotor again only 15k miles later because of a couple misfire codes that popped up recently. Pulled off the distributor cap (after only a year and a half of use since new) and it had signs of arcing all over the place (see picture). Codes went away after replacing components.
- Replaced fuel pump (original failed) and fuel pump relay
- Replaced fuel filter
- Had fuel tank recall replacement performed, replaced all related fuel/evap hoses while in there.
- Had injectors and upper engine “seafoamed” by my indy Volvo mechanic using B&G solution/cleaner.
- Replaced entire PCV system, cleaned EGR port, and replaced PTC (came with Snaab air pipe)
- Replaced ECU (with proper Bosch 628 “R” ECU)
- Replaced both O2 sensors
- Cleaned, then replaced MAF
- Had intake and exhaust system tested for vacuum/exhaust leaks and repaired all detected leaks.
- Replaced stock ignition coil with MSD coil
- Replaced intake air filter (then later upgraded to IPD short ram because whoooosh)
- Replaced TCV with IPD HD TCV
- Replaced entire Timing assembly (Belt, tensioner, pulleys, water pump) and ensured timing is set properly
- Replaced ignition switch
- Replaced throttle position sensor
- Thoroughly cleaned IAC (twice to be sure)
- EDIT (Consolidating information from further down thread) Did a compression test about a month ago, all within spec. Cylinders 1, 2, 3, 5 had readings of mid-high 170s, cylinder 4 was mid 160s.
This problem has been there since I purchased the vehicle and has persisted through all of the upgrades/repair attempts, getting slowly worse. Any ideas or recommendations would be infinitely appreciated.
