gs 300 misfire and cat glowing

[mikey-B]

Hi Guys .got a 1999 gs300. Problem started with it running a bit rough. Mechanic plugged it in and said it was the TPS..i had a 1998 gs which was running but had bodywork problems so i swapped the tps but it seemed the same so i put it back and  i changed the whole air intake unit then reset the tps position until i had the tickover at 800.The car seemed ok and revved freely so took it on the road . Got about 250 yards when it started to misfire, returned home and when i was stationary it was revving freely so ventured out again ...same problem. couple of days of the same but the misfire was getting worse. Swapped the plugs with the ones from the other car seemed to be even worse.Decided to change the leads, but these made it worse again, now it was almost undrivable. If i tried to drive it you could hear it popping in the exhaust. Plugged in again came up with Igniter, so changed it ...after a while it wouldn't even start. An auto elec said to try Easy Start to rule out a fuel problem managed to get it started with the spray but after about 4/5 mins keeping it going i looked down and saw the exhaust downpipe and cat glowing  so hot it was melting the under tray. Turned it off straight away. and here we are...i have looked through the whole forum before i posted this in case there were some possible solutions in previous posts. Any suggestions are welcome ....Cheers

[dwayneX]

Howdy buddy, not an expert here. See first if it is throwing any code. Also, have the fuel injector and catalyc converter checked.

[Bluesman]

When I suffered similar problems of a misfire with my LS400 it was one of the engines oxygen sensors and eventually the cat eventually failed with the inner core of the cat blocking the exhaust gases to exit the gas. Cat replaced  together with an oxygen sensor all back to normal. Hope this helps.