Help I Think I Broke My Rx

[UK Lexus RX300]

Please help.....

I have a 2002 RX300 with 125K miles which came up with a miss fire on piston number 5. Having checked out the forum I replaced the coil. This didn't seem to make any difference (check light and VSC light came on after 10 miles and the idle is rough) next I cleaned the airflow meter this seemed to help a bit but still coming up with an error and not right on idle. So today I have removed the air filter box and moved the throttle body out of the way to get to the back of the engine (I tried to remove the inlet manifold but cannot work out how to release it) anyway I have removed and changed the coil and plug for cylinders number 5 and 3 (back center and back right as I look standing in front of the car). Now the idle is OK but it doesn't change gear cleanly, holding rev's to the red line, then jumping up the road as it changes (almost feels like it is the rev limiter kicking in but at low revs) and the check light comes on with the same error (miss fire cylinder 5).

What have I done wrong

PS the car has had a LPG conversion and does the same on petrol or LPG which I think rules out the injectors

[smooth1]

Sounds like you may need to do a compression check on cylinder 5?

[Boxbrownie]

Hi, Did the car have "flashlube" fitted along with the LPG conversion, in my investigations on LPG and these cars it appears it is crucial to have flashlube fitted and working/topped up to prevent valve seat recession.......might be a possibility No5 has a damaged valve seat, could cause the symptoms you describe.

Best regards David

[UK Lexus RX300]

Hi, Did the car have "flashlube" fitted along with the LPG conversion, in my investigations on LPG and these cars it appears it is crucial to have flashlube fitted and working/topped up to prevent valve seat recession.......might be a possibility No5 has a damaged valve seat, could cause the symptoms you describe.

Best regards David

Thanks, I'll try a compression test next and talk to the LPG installer regarding flashlube. Still don't understand why it doesn't change up gear cleanly though. Any ideas?

[smooth1]

The shift points are controlled by more then just the MAF. The 02's are probably retarding the timing, and may be sending mixed signals for shift points.

Another quick test you can do is wait until the engine is cold. Then start it, and run it for about 30 seconds to 1 minute. then shut it off, jump out and put your hands around the exhaust manifold for each cylinder. If #5 is cold and the rest are warm, then you know you not even getting spark then also.