I have a 1989 Toyota pickup truck, 22R 4 cylinder with a 2 barrel carb. and manual transmission. It currently has about 215k miles on it. At 160k the engine was torn down and looked really good so no major changes were made. The problem I’m having is the engine idles really hard, sometimes it shakes pretty violently. I checked the vacuum lines, ignition timing, air filter, pcv valve, thermostatic air cleaner, and sprayed the carb with cleaner. I took off the old egr valve (which was clogged with carbon) and replaced it. I then set the idle speed to the specified 700 rpm. The problem is the engine still bounces around and the engine speed goes up and down between 600 – 800 rpm, sometimes jumping as much as 60 rpm at a time. When the engine first starts up it runs ok, but once the fast idle cam disengages it runs rough and lopes. When I accelerate it runs ok and does so even for a few seconds after I let off the gas but then it runs rough and lopes. Does anyone have any idea what the problem is?

i think that ur problem is inside ur motor.. no outside changes will fix that. if the motor was torn down ur chances r that somone messed up somwhere along the lines. theres only 1 way to fix that :(

This is a bit of a long shot, since you said you checked the timing....but what about a worn timing belt.

Try spraying around the intake manifold and base of carby with crc or wd40, if the engine note changes then you have a vacuum leak in that area you just sprayed. Failing that, you say it surges at coast throttle on the road? Have you changed the jets in the carby (primary jets), or changed the carby from original lately? Has the problem surfaced soon after a mod you have done (or had done) or did it creep in slowly, or just by itself? Answers to all these questions will tell you roughly where the problem may exist!!

Good luck finding your problem,
Mechdave...

When the engine is surging step on the brake to see if the speed of the surge changes. If it changes it means you have a vacume leak. Then do the wd-40 spray test mentioned above to find the leak. Often the seal on the valve cover leaks or carb gasget leaks if carb has been removed... also lose bolts on carb.

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I've got the same truck, but only w/ 109k miles. This truck was owned by my family at around 102k, and honestly, I love this truck. The feel of it as it drives is excellent, and it's a torquey beast for such a 4cyl.

I do have the same problems. The idle is erratic sometimes, and my truck going into neutralafter it's warmed up and I start it again without at least an hour cool down, will shut off. The idle is erratic, esp during "coasting" or trying to go 45 and stay going 45mph. As I slow down, the truck will also shut off, as if the idle ceases to exist.

When pumping my brakes, it does change the idle on my truck (when its not warmed up and shutting off.) So if your experiencing anything like me, you may have a vaccuum leak too. I know that I am somehow missing a bolt on the intake manifold of my truck which I just noticed last week, so it looks like I'll be replacing that soon.