[skipr]

Originally Posted by JStrong

skipr,

I'm not familiar with a leakdown test...care to explain?

I do not have any misfiring at all or at any RPM, just cyclical idle. Using Top Engine Cleaner several times has seemed to exacerbate the problem somewhat. When I accelerate slowly, or decelerate slowly, the truck will stall to a low idle, recover to a higher idle, stall again, recover, in a cyclical manner so that the truck will surge, slow, surge, slow, etc. when in gear so that my head and that of any passenger will bobble when in this low idle state.

If you were to look at my hydrocarbon emissions profile you would see spikes in hydrocarbons at low speed acceleration and deceleration. Hydrocarbons are well within acceptable limits elsewhere. These spikes are what are causing my emissions failure.

Carbon Monoxide and Nitrogen levels are well within the limits.

I'll keep your mechanical reasoning in mind as I progress...Thanks!

BTW, I haven't mentioned this before...only because I figured it was due to burn spots on my starter...but, I am having problems starting the truck. It may be unrelated, but maybe not. Whether the truck is warm or not, four or five seconds of seemingly torcherous starting is required to turn the engine over. It may be a combination of engine performance at low idle and starter problem because when I try to start the engine the new battery I installed less than 4 months ago seems like it is on its last leg. During the process of starting the truck sometimes it will turnover quickly as if the starter is positioned on a good spot on the starter, but most times it turns sluggishly all through the starting cycle. In all cases it takes a few seconds for the engine to start up.

A leakdown test is opposite of a compression test, it uses compressed air to force down your spark plug hole while at TDC, you will need the proper tool for this (just like a compression tester but reversed).It's more revealing than compression test, it pinpoints the leakage either through intake, exhaust or rings.