hesitation 85 tercel 4x4

[tealindy]

My little car is an 85 4x4, SR5 wagon, 5 speed manual.
It starts fine, although like me not fond of cold weather, but the problem is that as i am driving it has this little hesitation off and on.
It will seem to have full power one minute then start acting like it has limited power for a few seconds then zoom off we go again.
it is driving me crazy and I really need to have consitant power not just intermitant power. Sometimes i have to drive 60 miles a day for work.
I have had suggestions that I replace the carburetor, the O2 sensors (I did not know it had), and it could be a computer part (I did not know this car had a computer, I dont see a place to check the diagnosics). OR something with the Vacuum??
Any suggestions, I really hate to get rid of this little car, it starts and idles fine and is a go anywhere car. 225K original miles

[Petros]

who ever suggested those things you should ignor, they do not know what they are talking about.

sound like you just have a vacuum leak, and the likely cause of the problem. get a copy of the vac routing diagram from elsewhere on this forum and follow all of the vac lines to veryify they are all plugged in and routed correct. It does not take that long if you do it systematically.

if you find nothing than try using a can of carb cleaner, with the sir filter off and the vac line that goes to the underside of the airfilter capped off (I use a screws in it). Than spray some carb cleaners at the various parts of the vac line system, if you use Gumout brand, it will speed up the idle speed (test that by spraying a bit down the carb). Most brands will slow the idle speed. either way it will give you and idle speed indication of where the vac leak is. It could also be in the vac advance of the distributor or even the brake booster. If they are bad they will act like a vac leak. also check where the carb bolts to the manifold, and where the manifold bolts to the head. sometimes the temperature cycling will work the bolts loose.

It is possible the accelerator pump in the carb is bad, or the AAP diaphram. You check if the accelerator pump by looking down the carb (engine not running) with a flash light and pump the throttle hard, you should see a stream of fuel squirting down the throat of the primary barrel. If it dribbles or is intermittent, you need to replace the accleartor pump. You can get a rebuild kit for the carb and rebuild the whole thing, but I have just replaced the pump plunger and solved the problem. You can do it without removing the carb, you just removed the top of the carb (careful with the tiny parts! there are small clips on the linkage that are easy to loose).

These cars have a simple fuel controller, like a computer, but it is just a simple relay box that turns on and off some solenoids to adjust the fuel/air ratio. these are usually pretty reliable and usually do not cause that kind of a flat spot when they malfunction. There is also an O2 sensor to send a signal to the controller, but it is rare they go bad because these are much less sensative devices compared to the modern ones. yes they go bad, but it is rare and they do not cause a flat spot when they do.

You can also go check out the fuel system trouble shooting guide in the on-line factory service manual in this forum and find what systems yours match. and it will tell you what to check. the tests are simple and easy to do, no reason to be intimidated about finding the cause.

[tealindy]

Wow, that was wonderful advise. I
I will tell my son (our shadetree mechanic) and hopefully he will be able to use this info to get it fixed.
thanks so much.

[dlb]

tealindy, give us more details about when the problem occurs. does it happen when the engine is cold, warming up, or fully warm? does it happen at part or full throttle? details like these will help point to which emissions components could be the problem, or if it's a vacuum leak, or a clogged fuel filter, etc.

do not just replace the carb. that is a mistake that many mechanics make, simply because they don't fully understand these old carb and emission systems, but the carb itself is usually fine. and like petros said, the 'computer' on these cars (if you can call it that) is super simple and generally very reliable.

[Petros]

it is always important to diagnose the problem before you try and fix it. You could replace a lot of good parts thinking you are fixing it, but than you will still have the problem.