Making this post in a last-ditch ideas effort before tearing into the rats nest when winter arrives. Pretty sure is a primary injector leaking but don’t want to risk disassembling the rats nest if I can help it. I apologize in advance for the essay...
Problem Statement:
Idle seems rough when dipping down to ~800rpm but oscillates 50-100 rpm at about1.5-2hz. Its noticeable enough to vibrate the car. Further to this holding revs at 3krpm stationary is fine for a couple seconds then starts to break up a little similar to how the idle oscillation comes on. Additional symptom is poor fuel consumption (best case estimate 20mpg motorway, average calculated around 16mpg including some local and some motorway driving, uk gallons). Also about a 30% rate of an exhaust pop during shifting around 3k just gentle street driving. Occasional pop when the cold high idle/cat warm up disengages too.
I am almost certainly being a bit too anal about this and could just raise the idle and be done with it, but it would be nice to not burn through AS much fuel on longer trips and in case the catalyst ends up shitting the bed because of the popping.
Background info:
Engine etc is completely stock 99 spec, bar an RB cat back and BUR9EQP plugs all round. Seems like the car may have sat for up to 10 ish years prior to a couple years ago. Fuelling issue corrected last year with new pump and filter prior to my ownership. Car runs and boosts fine on throttle, cruising etc. just the consumption is high. Cold starts fine, hot start occasionally stumbles around 500 but after a touch of throttle to get it above 750 it gets into the oscillation and remains there or higher without issue. Idle screw is likely a little out as it acts ever so slightly differently each time adjusting. Compression checked last year in the 7s all round.
FSM troubleshooting from F-178:
Rough Idle when warm (could just be oscillating coming across as rough though): PRC Sol Valve, Fuel Thermosensor
Idle Fluctuation/Hunt: Idle control valve, Primary injector, spark plugs, ignition timing
Fuel economy: Air cleaner element, Primary injector, fuel pressure reg, 3-way catalyst
The only repeat cause is a primary injector so leaning towards that.
Actions taken so far:
Throttle body readjusted (lower plate adjusting screw was slightly open instead of shut). Plate adjusted until TPS stopped receiving changes, then increased 1/8 to 1/4 turn so its not completely in forced contact with the bore. Also adjusted the throttle cable with a little bit of slack just in case. TPS then adjusted back into position, narrow band dead on 1V, wideband 0.53v to 4.32V (struggling for memory on those but slightly above and below nominal respectively). Thermowax working fine too.
Then had fun readjusting the idle set screw. With high idle it does not oscillate but a bit of intermittent burble. During adjustment I could get the car to stall out closing the adjustment screw, and get it over 1.2krpm so pretty sure there are no vacuum leaks based on that.
It is smoother (no oscillation) when the test pin is connected to stabilise the IAC valve etc. (may have seemed slightly rich though still but not entirely sure) After an ecu reset it was quite smooth for a bit including testing with the IAC valve disconnected, went for a drive and it was back to oscillating. Not switched the car on since that but want to try disconnecting the IAC while its oscillating to see if it instantly stops it.
IAC valve has been removed and cleaned (only a touch of surface soot in the output side and after some carb cleaner looked new. Valve was seated with a bit of preload but some pulling on it starts to open it too so not blocked. Did not apply voltage to it to test actuation though.
New O2 sensor in, identical symptoms before and after the change.
Rotor 2 plugs look fine (about 1-1.5k miles old). Been too lazy to get the front rotor plugs out just yet, but need to at some point.
MAP sensor readings (engine cold and off) are within 0.07V of nominal scaling. Used disconnected vac pipe and a vac pump and gauge to test without unknown engine vac level.
No engine codes, did have a code 56 a while back but cleaned the exhaust ground up as a precaution and seems fine now.
Ran some BG44k through it too, one can to 1/8 tank and let it sit a few days, one can to ¾ tank into normal driving as has been recommended in one or two places. No change in behaviour beyond what could be attributed to the variation I get.
Fuel pressure (incoming line from firewall has a gauge in place) depletes to zero pressure within 24hrs (want to check it over shorter periods too for more data) of shutting the car off. Normal 2 and a bit bar when running otherwise.
Think there may be one or two things I’ve done but forgotten about, and my apologies again for the essay. Any input over the next couple months would be greatly appreciated, TIA.
Problem Statement:
Idle seems rough when dipping down to ~800rpm but oscillates 50-100 rpm at about1.5-2hz. Its noticeable enough to vibrate the car. Further to this holding revs at 3krpm stationary is fine for a couple seconds then starts to break up a little similar to how the idle oscillation comes on. Additional symptom is poor fuel consumption (best case estimate 20mpg motorway, average calculated around 16mpg including some local and some motorway driving, uk gallons). Also about a 30% rate of an exhaust pop during shifting around 3k just gentle street driving. Occasional pop when the cold high idle/cat warm up disengages too.
I am almost certainly being a bit too anal about this and could just raise the idle and be done with it, but it would be nice to not burn through AS much fuel on longer trips and in case the catalyst ends up shitting the bed because of the popping.
Background info:
Engine etc is completely stock 99 spec, bar an RB cat back and BUR9EQP plugs all round. Seems like the car may have sat for up to 10 ish years prior to a couple years ago. Fuelling issue corrected last year with new pump and filter prior to my ownership. Car runs and boosts fine on throttle, cruising etc. just the consumption is high. Cold starts fine, hot start occasionally stumbles around 500 but after a touch of throttle to get it above 750 it gets into the oscillation and remains there or higher without issue. Idle screw is likely a little out as it acts ever so slightly differently each time adjusting. Compression checked last year in the 7s all round.
FSM troubleshooting from F-178:
Rough Idle when warm (could just be oscillating coming across as rough though): PRC Sol Valve, Fuel Thermosensor
Idle Fluctuation/Hunt: Idle control valve, Primary injector, spark plugs, ignition timing
Fuel economy: Air cleaner element, Primary injector, fuel pressure reg, 3-way catalyst
The only repeat cause is a primary injector so leaning towards that.
Actions taken so far:
Throttle body readjusted (lower plate adjusting screw was slightly open instead of shut). Plate adjusted until TPS stopped receiving changes, then increased 1/8 to 1/4 turn so its not completely in forced contact with the bore. Also adjusted the throttle cable with a little bit of slack just in case. TPS then adjusted back into position, narrow band dead on 1V, wideband 0.53v to 4.32V (struggling for memory on those but slightly above and below nominal respectively). Thermowax working fine too.
Then had fun readjusting the idle set screw. With high idle it does not oscillate but a bit of intermittent burble. During adjustment I could get the car to stall out closing the adjustment screw, and get it over 1.2krpm so pretty sure there are no vacuum leaks based on that.
It is smoother (no oscillation) when the test pin is connected to stabilise the IAC valve etc. (may have seemed slightly rich though still but not entirely sure) After an ecu reset it was quite smooth for a bit including testing with the IAC valve disconnected, went for a drive and it was back to oscillating. Not switched the car on since that but want to try disconnecting the IAC while its oscillating to see if it instantly stops it.
IAC valve has been removed and cleaned (only a touch of surface soot in the output side and after some carb cleaner looked new. Valve was seated with a bit of preload but some pulling on it starts to open it too so not blocked. Did not apply voltage to it to test actuation though.
New O2 sensor in, identical symptoms before and after the change.
Rotor 2 plugs look fine (about 1-1.5k miles old). Been too lazy to get the front rotor plugs out just yet, but need to at some point.
MAP sensor readings (engine cold and off) are within 0.07V of nominal scaling. Used disconnected vac pipe and a vac pump and gauge to test without unknown engine vac level.
No engine codes, did have a code 56 a while back but cleaned the exhaust ground up as a precaution and seems fine now.
Ran some BG44k through it too, one can to 1/8 tank and let it sit a few days, one can to ¾ tank into normal driving as has been recommended in one or two places. No change in behaviour beyond what could be attributed to the variation I get.
Fuel pressure (incoming line from firewall has a gauge in place) depletes to zero pressure within 24hrs (want to check it over shorter periods too for more data) of shutting the car off. Normal 2 and a bit bar when running otherwise.
Think there may be one or two things I’ve done but forgotten about, and my apologies again for the essay. Any input over the next couple months would be greatly appreciated, TIA.
