FOR EVERYONE READING THIS IN THE FUTURE: The resolution of the issue is described and detailed in post #36 on page 2 of this thread.
Apologies in advance for a long post. I have exhausted my knowledge and things to try so I'm asking collective forum wisdom for ideas. Please read below and let me know if you can think of anything else.
The car
1993 US-spec B36 w/130k miles, and very good maintenance history. Multiple valve adjustments in the past, timely oil changes, etc. Completely stock aside from Dinan chip installed years ago. The car has been sitting for the most part of 3 years before I bought it (less than 900 miles in the last 3 years), but it did drive some, obviously.
Issue
I have a lumpy idle, cyclical, worse when car is fully warmed up. There is a bit of an engine shimmy when it idles, the best way to describe is it "stutters" a bit every couple of seconds. If I sit in the car, I can feel it shake, and see gear lever vibrate. It is noticeable when looking at the engine that is not running 100% smooth, and you could see it visually shake a bit.
Idle rpm is correct 950+/-, car never dies, always starts the first time (though cold starts take a bit longer), and overall runs good - makes good power, revs smooth, drives well. There are no lights on the dash or codes stored.
What have been done and tried so far:
Ignition system: Replaced distributor cap and rotor with new Bremi parts, new Bosch coil, new correct Bosch Y6DC plugs, and brand new set of OE spark wires with new donut sensor.
Fuel system: Replaced all fuel lines under the hood, cleaned injectors - new o-rings/pintle caps, etc, replaced FPR with correct 3 bar unit. Replaced fuel filter with new Mann unit. I did not check the fuel pressure, don't have the gauge.
Air intake: New air filter, new intake temp sensor, cleaned MAF, made sure intake boot has no tears, etc. The intake plenum was taken off, and every o-ring, vacuum line, and hose was replaced with new. I cleaned ICV while there, tested check valves, and made sure everything was connected correctly. All was put back together and smoke tested - there are no vacuum leaks (aside from tiny leak from throttle body butterfly bearing shaft - but let's ignore it for now). I have also replaced O2 sensor with brand new Bosch unit, and after that balanced ITBs with Carbtune tool and tuned all 6 to show 22.3cmHG. Intake resonance flap self-test works as it should.
In addition, the following things were done: fresh oil/filter, new Hella coolant temp sensor (blue), checked all grounds. Cleaned crank position sensor (tested ok), throttle position sensor clicks when throttles open, tests ok with multimeter.
None of the above made ANY difference in how the car runs. By no means it is bad, but it does not feel 100% right. There is a faint whistling/whining sound, coming from the front/bottom of the engine when I press gas pedal and engine revs - both at idle and while driving - I can't pinpoint it. Don't know if this is a factor or something I could check. I have access to lift. I'm a very capable shade tree mechanic. I'm lost as to why this still runs lumpy/shakes.
Apologies in advance for a long post. I have exhausted my knowledge and things to try so I'm asking collective forum wisdom for ideas. Please read below and let me know if you can think of anything else.
The car
1993 US-spec B36 w/130k miles, and very good maintenance history. Multiple valve adjustments in the past, timely oil changes, etc. Completely stock aside from Dinan chip installed years ago. The car has been sitting for the most part of 3 years before I bought it (less than 900 miles in the last 3 years), but it did drive some, obviously.
Issue
I have a lumpy idle, cyclical, worse when car is fully warmed up. There is a bit of an engine shimmy when it idles, the best way to describe is it "stutters" a bit every couple of seconds. If I sit in the car, I can feel it shake, and see gear lever vibrate. It is noticeable when looking at the engine that is not running 100% smooth, and you could see it visually shake a bit.
Idle rpm is correct 950+/-, car never dies, always starts the first time (though cold starts take a bit longer), and overall runs good - makes good power, revs smooth, drives well. There are no lights on the dash or codes stored.
What have been done and tried so far:
Ignition system: Replaced distributor cap and rotor with new Bremi parts, new Bosch coil, new correct Bosch Y6DC plugs, and brand new set of OE spark wires with new donut sensor.
Fuel system: Replaced all fuel lines under the hood, cleaned injectors - new o-rings/pintle caps, etc, replaced FPR with correct 3 bar unit. Replaced fuel filter with new Mann unit. I did not check the fuel pressure, don't have the gauge.
Air intake: New air filter, new intake temp sensor, cleaned MAF, made sure intake boot has no tears, etc. The intake plenum was taken off, and every o-ring, vacuum line, and hose was replaced with new. I cleaned ICV while there, tested check valves, and made sure everything was connected correctly. All was put back together and smoke tested - there are no vacuum leaks (aside from tiny leak from throttle body butterfly bearing shaft - but let's ignore it for now). I have also replaced O2 sensor with brand new Bosch unit, and after that balanced ITBs with Carbtune tool and tuned all 6 to show 22.3cmHG. Intake resonance flap self-test works as it should.
In addition, the following things were done: fresh oil/filter, new Hella coolant temp sensor (blue), checked all grounds. Cleaned crank position sensor (tested ok), throttle position sensor clicks when throttles open, tests ok with multimeter.
None of the above made ANY difference in how the car runs. By no means it is bad, but it does not feel 100% right. There is a faint whistling/whining sound, coming from the front/bottom of the engine when I press gas pedal and engine revs - both at idle and while driving - I can't pinpoint it. Don't know if this is a factor or something I could check. I have access to lift. I'm a very capable shade tree mechanic. I'm lost as to why this still runs lumpy/shakes.
