Thread: Persistant misfire at idle, stalls at idle in gear

The Vehicle: 1987 Range Rover Classic, 3.5 Injected V8

The Problem: Persistent misfire at idle, stalls if idling in gear, but fine throughout the rest of the rev range.

Steps I've taken (In no particular order):
* New rings all round - some were literally broken
* Valves have been lapped in
* Full VRS kit installed
* All brand-new tappets, original tappets worn correctly, so cam should be fine too
* Rockers and rocker arms unclogged, I could have been in a black & white minstrel show when I was done
* Injectors tested for leaks at far above standard fuel pressure
* New injector o-rings
* Tried a spare AFM (Lucas 2AM Flapper)
* Tried two spare ECU's
* Throttle pot tested fine (DMM)
* Rave ECU troubleshooting followed to the letter
* Leakdown tests
* Compression test post-valve lapping 125 PSI on each cylinder, it's low, but yay me! The previous figures were all uneven and as low as 90 PSI, comp ratio 8.13.1? Best i can make out on the stamping, not all characters are completely readable
* Ignition timing checked, and checked, and checked, oh and checked, and did I mention i've checked lol, could do it blindfolded by now, btw I'm starting from 6deg adv
* Distributor rebuilt
* Distributor pickup coil replaced - old one dead, completely, believe me and the Sunshine Motorway
* Distributor stator replaced
* Rebuilt distrutor into a donor housing, swapped base plates after cleaning and reconnecting bob weights, skipped the nylon locking ring for now, still works installed pickup coil, gapped to 0.203mm (smallest in my brass gauges)
* Tried spare coil
* New ignition leads all round
* Tried two brand new sets of stock spark plugs
* Now using Bosch four-earthed plugs (don't ask me why, i like 'em, they work great in the falcon, misfire was still there on two other sets of stock plugs)
* Fuses and Relays fine
* Gas analyzer on exhaust - tune the AFM & CO 1.5%
* Heads cleaned and reinstalled (with new gaskets, part of VRS kit)
* Valley Gasket replaced
* Leaking oil pressure switch replaced with new
* Replaced ECU harness
* Installed a spare tach (dash one won't work, taking tach signal from line attaching ECU to coil because my instrument clusters electronics don't match any wiring diagram i've found to date, including rave)
* Tried a Jaycar Digital Tachometer kit which seamed to kill all spark for some reason - yet to investigate that one
* Bosh ignition amplifier conversion (not me, but I just rewired it this morning)
* Alternator charging fine, keeps the battery topped up and believe me it's being well and truly abused at the moment with the constant starting and stopping
* Rebuilt starter motor after one of the brushes broke lose from it's mounting
* Yesterday I found running vac advance at manifold pressure, instead of throttle body pressure smoothed it all out as in totally gone, problem solved, tried more advance by timing light instead so I could put the vac lines on properly, didn't have same effect, I didn't have a T-Piece for the vac line, so I couldn't attach FPR, it drove and idled perfectly in gear, at stop lights without stalling, just had no power going uphill, i'm guessing because of the lack of FPR-Vac, doesn't matter, replaced all ignition wiring (pickup to amp, amp to coil, ign to coil) with new 3mm Twin-Sheath, soldered and heatshrunk crimps and gapped the pickup coil and stator today and things just got worse
* Brand new fuel pump
* Brand new fuel filter
* New fuel
* Higher octane fuel
* E10
* Regular unleaded
* Misfire seems to minimize when AFM removed, but still noticeable, still stalls at the most inopportune times
** More info **
* No O2 sensors on this model, no Onboard Diagnostics either
* No idle control valve on any of my three manifold sets nor is there provision in the wiring harness
* Non tune resistor on this model... i've got one, i plugged it in... wouldn't start... removed... kept for a trophy

I've basically gone through all this rigmorole to sort out bad fuel efficiency to begin with (was only getting 200km per full tank), but this misfire at idle has me completely stumped, I've been working on it for months!

Does anyone have any ideas? Something I've missed or overlooked? Underlooked? Something completely bizarre and out of this world like really giving VB that good college try instead of a real beer? *digs* Something completely obvious?

I love driving the Rangey, just hate having to either hold some throttle at traffic lights or risk stalling. Any help / ideas greatly appreciated.

Having the fuel pressure vacuum hooked up or not won't change the full power as WOT has no vacuum anyway. All that happens is that it runs rich at light load, all other things being correct. If you have the dissy vacuum connected to full vacuum, as the idle revs drop the vacuum drops, timing retards and that increases the rate of stall.

Make sure your pickup-to-ignition module wires are well away from the alternator or electrical interference will play havoc with the spark.

Adjust the idle speed up by using a 3/16" allen key in the recess on top of the throttle body.

Flip the plastic cover off the MAF, then run the engine, and gently manipulate the wiper arm and see if it runs better at different positions than the one its at. You can change the spring position so that the wiper arm is where it runs better. Try different positions and test drive. I've done this a few times on these horrors, it makes all the difference.

Oh and the stock RR tacho runs off a tapping inside the alternator, white/grey wire. This wire won't run a regular tacho.