Hey guys, i've got a 1988 Corolla SR5 2-door Coupe with the 1.6L 4A-F Carb California model. It has 196,xxx miles on it, and I just changed the oil, flushed the coolant, changed the tranny oil, fuel filter (the paper one under the hood) and air filter. I also replaced the spark plugs (got NGK Laser Platinums) and wires/cap. I used some SeaFoam down the carb throat and it seems to be running much better. I've done a few medium distance drives (2x 230 miles) and averaged 36.5MPG (before the tune-up) and 37.6(after the tune-up.) The car has decent power, and drives trouble-free when cold. After about 2 minutes (this thing heats up much faster than my old diesels :-P) once it's warm, it still has roughly the same power, but hesitates/bucks very slightly while accelerating. It only seems to occur from about 1800-2900 RPM, before and after those RPMs it has smooth power. It's not a huge issue, but i'm guessing it either needs a carb rebuild (or maybe just tuning?) and/or the ignition timing is off. Sometimes (maybe 35% of the time) the engine will diesel a little after being turned off. Not for long, just maybe 1-2 seconds of "sputtering" after the key is turned off. Overall a great little car, and the issue does not keep me from enjoying it by any means, but it would be a nicer drive if it didn't jerk like a cold motorcycle while accelerating!
Should I try rotating the distributor a little to retard the timing? Or should I take it to a shop and have the carb rebuilt and tuned? I use the term "tuned" very generally, I just mean for someone to adjust it all properly, lol. Thanks in advance!
I Have a 88 Corolla with the 4AF and it also intermittantly deisels when its shut off. Checked the timing and that was fine.I also have paperwork from my car from the original owner and the car was brought to a mechanic in 93 for deiseling issues, so 18 or so years later its still doing it.
I think its the carb, was thinking about doing a weber 32\36 but i think i will do a 4age swap before i go that far with this motor.
I also had hesitation and bucking issues when the motor was cold and it turned out it was my thermostat, it was stuck open so some of the thermo vac switchs would not open\close. Might be somthing to look into, thermostat is like $4.
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What would be the best way to go about checking for vac leaks? Soapy water? They all appear to be in pretty good condition, as if they were replaced within the last few years. Thanks again!
In particular check that vac lines are connected between egr and vac modulator next to it and the vac advance lines at distributor. Just make sure all arr connected in place. If the idle speed is set too high that can also aggravate the dieseling.
All the vac lines appear to be connected fine. Engine runs rough if i disconnect the vac. advance on the dizzy at idle. Also, idle is about 1300, and I backed the idle adjuster out so far it came out! Didn't go down at all while I was backing it out either. It would go up when I would tighten the adjuster (to what sounded like about 1700 RPM) then it backed down to about 1300 after I backed the adjuster out again, but wouldn't go lower than that. Should I rotate the distributor a little CCW to retard timing a smidge?
If backing out idle speed screw has no effect on lowering idle you have other issues. Check to see that the choke is fully off once engine is warmed up. The butterfly flap in carb should be vertical. If not the electrical heater in choke could be shot or the butterfly plate or linkage could be gummed up and needs cleaned with carb cleaner. Another possibility is the dual diaphram throttle positioner. It's on passenger side of car. It has a linkage with two tho three vac lines attached. It elevates idle when a load is placed on it (lights, turn wheel and load up p/steering etc.) and it also holds open throttle for a short time when you decelerate. To adjust it have someone help you start car and then while you are looking at positioner have them turn on lights. You will see linkage move and you can adjust speed down if engine races with lights on. Check all hoses that are attached to the positioner to make sure none leak. Here is a link for reference only (different vehicle) that shows the throttle positioner.
The idle elevates slightly when loads are placed on the engine (slight drop then it kicks in and RPMs go to normal). I took some pictures while I was under the hood, and was hoping someone could explain to me what i'm looking at as far as the carb. setup is concerned. The throttle body looks pretty dirty, and looks as though it's only held on by 4 bolts? Seems like it would be pretty easy to clean...
That last pic shows a vac connection point ( metal tubing)) with nothing attached to it. Could cause a vac leak which might account for your probs. Take a look at vac diagram underhood to see what it is supposed to be connected to. If you pull that carb be sure to note where that jungle of vac lines go to make it easier on the reinstall.
That last pic shows a vac connection point ( metal tubing)) with nothing attached to it. Could cause a vac leak which might account for your probs. Take a look at vac diagram underhood to see what it is supposed to be connected to. If you pull that carb be sure to note where that jungle of vac lines go to make it easier on the reinstall.
That connection does not go anywhere, if you look inside the end of that connection it does not connect into the metal line it just sits around it, thats how it is on my car anyways.
On a side note i would just spray some carb cleaner down the carb, did it to my car when i got it (looked like yours inside the carb), cleaned all the crap off and it's 100% cleaner, looks new now.
I have used some SeaFoam, mainly because I feel safe about having that stuff go into my cylinders. What about carb. cleaner? If I use it very liberally to really clean it out should I try and use a cloth/paper towel to soak it up and prevent it from being combusted? With SeaFoam I sprayed it in while it was running, I assume I wouldn't want to do that with carb cleaner?
BTW the throttle body is REALLLY dirty... wouldn't be surprised if using carb cleaner fixes my problem... Didn't really notice just how dirty it was when I was using the SeaFoam.
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Rolly
Possible Timing Issue or Carb?
Linear Mode
