Decided to replace my injectors since I had a reconditioned set, and the car still has the flat spot during acceleration at about 1500-2000 RPM. So cleaned out the stepper valve as well, new HT leads and general tidy up. All good car started first time idle was smooth, result!... No.... when the car warmed up idle at 2000rpm.
Ok disconnected the stepper valve hose from the throttle body and could hear is sucking strongly. blocking the pipe killed to engine so no other air leaks causing it. Reset the TPS. no difference. Ordered new Stepper, old one jammed open. When it arrived replaced it all great, good idle but flat spot still there. So decided to take the car out for a run, now it refuses to idle at all. Did TPS reset etc still nothing, warmed the car up and idle was there albeit erratic and the revs would drop off to almost 0. Oh well can't harm, decided to reset the the engine management, disconnected the battery took the opportunity to clean up the contacts and the earth connection, waited about half an hour and reconnected the battery, re synced the key fobs and started car, idle perfect.
Still good idle a week later and throttle response good with the cleaned injectors. Flat spot still there, this is really baffling, the internet is full of people with similar problems but no one has come up with a clear fix. I need to get this sorted pulling away from junctions can be traumatic when the bogging happens, lifting the throttle can help but not always so not sure if too much fuel or air.
To date I have changed. Coil packs, HT Leads, Cam sensor, MAP sensor, Plugs, cleaned all connectors, Replaced the throttle body with 52 mm version, induction air filter, new fuel filter. I have a new lambda sensor, coolant sensor and crank position sensor left to do. Lambda sensor will go on the new stainless 421 exhaust when it arrives. ODB gives no faults, although the temperature seems to read a bit low (86 to 95 during normal driving, outside temp 25 degrees) which could cause over fueling, I do get the occasional backfire after the bogging down.
Long post, Sorry, any one experienced this? Any confirmed fixes?