I have a 1993 JDM Toyota LiteAce pick up with a carbureted 1.8 2Y inline 4-cylinder gas engine. It is an OHV with a distributor with an internal coil. It currently has 27,000 original miles on it. The issue I am having with it is when the engine is cold, it stutters/shudders and hesitates (misfires) under light throttle (under wide open throttle it smooths out or isn’t noticeable). It backfires through the exhaust something fierce when coasting in gear (off throttle or compression braking), usually until it has an especially powerful backfire, after which the hesitation and sputter goes away, and it no longer backfires for the rest of the drive. This typically takes 5-10 minutes. It seems to do this worse in cooler weather, but still happens in warm weather. I can also turn the engine off, let it site for 5 minutes, restart and it runs fine. The problems return after it sits for a few hours and cools off.

Compression tested and all cylinders were within 10 PSI of 150. I pulled the valve cover; all lifters appear to be working, the push rods are all straight and all travel freely and rotate. I pulled the spark plug wires individually while the engine was running to check for changes in idle. With #1 the idle speed dipped significantly, and it ran noticeably worse. With #2 there was no change in idle. #3 and 4, the same drop in idle as #1. So, the problem is isolated to #2. I hooked up a timing light to the #2 plug and wire, and it is getting spark. I swapped spark plugs with #1 cylinder, and the problem stayed with #2. The #2 plug was wet from fuel. After driving for enough time to get it to backfire and smooth out, I again pulled the #2 plug wire, and the idle dropped and then ran worse. How can this be happening?

I replaced the cap, rotor, plugs and wires for good measure, not really expecting a difference. No change. After that I swapped the Ignition control module (or Igniter as they call it in Japan) with cheap unit from Amazon, and it wouldn’t start at all. I reinstalled the original Toyota. Runs the same. So that could just been a bad new part, which is not uncommon these days.