Hi, my 99 LT has suddenly started misfiring for the 1st couple of miles after a cold start. Have replaced distributor cap, rotor, wires & plugs but it has made no difference. There are no stored trouble codes either. Seems to be worst at light throttle - if I floor it it runs fine, it also idles perfectly when cold. Once things have warmed up everything is fine. Any ideas would be appreciated.

 

Have you cleaned the EGR valve, MAF sensor, and/or throttle body (including the removal and cleaning of the IAC valve)? If not, I would recommend all of the above.

 

Thanks for the advice - I will start with the EGR valve as that is the most accesible. I think I wasted my time changing distributor cap, rotor, plugs & wires as it has made no difference + the old components didn't look too bad. Must have been the most inaccesible distributor cap on any vehicle I have ever owned. Would have been much easier if I had removed the heater hoses but I didn't fancy disturbing them unless I really had to. Will post if there's any improvement. Just taken vehicle on a 15 mile run & it did the same, started off OK then started missing on light throttle after half a mile or so before settling down after about 3-4 miles. No problem when hot. Weird thing is, I got back from a 2 week motorcycle vacation last Friday so vehicle had been unused, was no problem before I went away, almost like something changed while vehicle was laid up? Very strange.

 

My 97 does the same thing...check if your heather hose is leaking and dripping on your coil wire thats what mine is doing...I dont know if RHD will be the same or not

 

Thanks for advice about heater hose big_blazer. Checked that & no leaks anywhere.
However, I cleaner the EGR today, took it off & didn't look too bad but cleaned everything up anyway & now - BIG DIFFERENCE! No misfiring & the slight fluctuation in idle speed that i've been having for months has gone too. Only problem is, while I was working in that area I noticed the tiniest little drop of coolant at the front of the intake manifold gasket - guess i'm falling victim to this common problem area, will leave alone for the time being as it really is tiny & dries up once the engine is warm. Water level doesn't seem to drop in radiator either. Guess i'm gonna have to face it sooner or later though.
I'm a little annoyed that I struggled for ages to change cap & rotor etc & wasted my time but hey, at least I now know they're new so won't have to touch things for a while. Truck has now done 79,000 miles so I suppose they were due to be replaced by now anyway. Thanks to everyone for their advice. this forum is a real lifeline for me as Blazers are so rare here in the UK & info is hard to come by. Most car part shops look at me like I just got off a spaceship if I mention that I have a Blazer.