Throttle Position Sensor Adjustment And Rough A245E Changes

Preface: I'm no master mechanic, just a knucklehead with a repair manual.

I changed the TPS, among other things, thinking it would increase the sluggish acceleration/performance in my 94 corolla dx 1.8L A245E 4-speed. Had I known it would cause the trans to change roughly, clunk, I would have left well enough alone. I used the manual and a multimeter to set/adjust within the parameters. The adjustments are quite fiddly. I tried to tweak-it, Nothing seems to help. And a extra bonus, the gas mileage has dropped into the teens, the speedometer seems to be off 10 MPH? The car has 205.000+ the car, mechanically seems sound. The South Florida sun has done a number on the paint/plastics. The car was given to me, it's a project, I'm retired. I have done a full tune-up, changed the distributor, air filter, new fuel filter, radiator, replaced cracked manifold pressure hoses, A245E filter/fluid change, oil/filter change, tried Sea Foam through the fuel system to clean as best as it will, 3 times. It had a bad vibration in the cockpit at the steering wheel, changed the motor mounts/trans mounts. ball joints, tie rod ends, sway bar ends front and rear, muffler hanger bushings, struts on all 4 corners, still have many more bushings. The suspension still has bumps and doesn't seem tight.

But I digress. My main concern is the engine/trans.

Any suggestions would be greatly appreciated. You guys know more than I.

max

Very possible that the TPS unit was damaged or now has a set bias. TPS does control shift points on the transaxle, no doubt about that. Trying to get it back, as you've seen, is the hard part.

Just curious - did you do a compression test? I'm concerned about the seafoam - I've used it in the past on some older outboard motors and some small motors, but I've seen this stuff cause all sorts of funky behavior on cars. All depends on how it was introduced, just in the tank, added to the crankcase, pulled through the engine via vacuum source? Possible it loosened a truck-load of carbon from the EGR system and that is causing poor running, making it harder to diagnose issues.

Bikeman982 was our resident 7th gen Corolla expert - he hasn't been on here in a while, but he may respond to PM. Might be worth pinging on him and see if he knows a trick or two.

Thanks for the quick reply. Question: If I replace the TPS, I did, should I look to other sensors as well? Seems they all report back to the ECM to control the engine functions. I tweaked the TPS and the shifts become smoother, but I can seem to find the sweet-spot. The idle is about 900rpms in park, 850rpms in drive. With the AC on the idle is 900rpms. I replace a cracked pressure hose that was causing a idle fluctuation .

No compression test, yet. The trans shifts were smooth before the TPS change, but the throttle response/acceleration was dismal. A turtle with bad knees! I'm sure there are multiple issues, my inexperience doesn't fill in the gaps. At 205,000 mile other sensors, etc. must need replacing. I'm replacing them in turn, they can be quite pricey. The person/women that gave it to me changed the oil and did scheduled maintenance until she purchased a new corolla. She used it in Miami city traffic and I-95. It sat for 2 years. I've been working on it for more than a year.

I ran the SeaFoam through the fuel 3 times then changed the fuel filter. I cleaned the throttle body with cleaner. I may replace the fuel injectors.

I put the measured amount into the oil and changed the oil after a few hundred miles and repeated, lots of sludge was expelled. The engine seem to run quite a bit smoother with less vibration through the steering wheel.

The engine is running smoother, it's just the transaxle clunk at 3th gear. I think we are a tweak away for just right. I'm sure you guys have run into this sort of thing, and have the trick. I'm trying to learn, but occasionally I get in over my head.

Thanks again,

max

Primary O2 sensor is likely shot or getting close to dying. Be first on my list of sensors to replace, especially since you've noticed lower MPG, even after all the TPS adjustments. Injectors could still be gummed up, especially sitting for that amount of time.

How's the spark? Did the plugs look OK when you replaced them, did you have a chance to pull the plugs and read them, see if anything changed? How did the throttle body look, pretty gummed up? I believe these models use a cold-start idle-up valve on the TB. That can sometimes get gummed up and cause the engine to idle a bit weird.

Sounds like the car needs to driven out - the old Italian Tuneup. Sitting for a long time hurts the car more than having tons of mileage on it. Since you mentioned the power was down at speed - my thoughts are replace the O2 sensor (use Denso branded ones if you can), and check on fuel system (pump, injectors, pressure regulator, injector log, etc.).

You can see if the O2 sensor might be at fault by running the engine WOT - in that case, the engine will default to an open-loop map, the ECM will ignore inputs from the O2 sensor and just go with the MAP and TPS sensor readings. If the car stumbles or is sluggish right before WOT but seems to "perk" up a bit once you floor the pedal, that really points to a possibly dead or dying O2 sensor.

Fuel system - on the fuel rail, there should be a schrader valve that you can attached a fuel pressure gauge - just to verify that you are getting good fuel pressure. As for injectors, harder to tell visually - there are some DIY guides online that show you how to clean them off the car. Might be worth a shot, or try a local pick and pull and see if you can get another set from a 7th gen cheap.

Great minds think alike. Forgot to mention, I installed a new 02 sensor. Injectors well be my next replacement, what do you think of rebuilt/refurbished injectors? I saw 4 listed at $80.00. I'm sure my O-rings/seals are perished. The throttle body was ok not visibly gummy, but with 205,000 mile I'm sure it gummy in places, I tried to clean with spray cleaner and a clean cloth.

I haven't removed and inspected the plugs, they only have a few thousand, if that. I will do that.

I had the same idea on the fuel system, check pressure, pressure regulator, etc. Manifold hoses, PCV looks ok, I replace the gas cap o-ring.

The cold-start idle-up valve, would that be the IAC/ISC valve? The symptoms would be similar, unstable idle, hesitation.

I know the Data Link info is rudimentary, at best, in these old corollas. What is your opinion on going to a dealership and having a diagnosis done on the engine? Do you think it a waste of money?

Thank you for your patience and sharing your experience, you have given me starting points.

Thanks again,

max

I took the old girl out on I-95 and, as my father used to say, "blew out the carbon". She still can wind up if you can find a long open stretch.

I looked at the member you were referring to he hasn't been online in a year.

Rebuilt/refurnished injectors should be perfectly fine. Four injectors for $80 is an awesome price. As for cold-idle, I believe that is part of the IAC system, but from what I gather, cold-idle was a separate entity entirely. IAC would bump the idle up when you kick on the AC, which from your earlier post sounds like it is working.

Diagnostic at a Toyota dealership - depends on the level of expertise of the technician. Since this is pre-OBD-II, you'll need someone that is well versed in old school diagnostic work. You've pretty much hit all the major things I would have checked myself. I'd say, short of swapping a bunch of parts off the car, might be worth the $85 or so to do a diagnostic. They might be able to find something when they put the car up on a lift.

I'd try pulling plugs first, see what they look like, swap in new injectors + o-rings (if they don't work, you can resell them pretty quickly), then run the nuts off the car on the highway, See how it runs, pull the plugs again and read them - see how much different they look. Sounds like the engine is still OK, other than the hesitation. Compression test would be a nice data point to have, but probably won't reveal too much at this point.

Its tough to diagnose cars that have been sitting for some time. Sometimes, they will "automagically" fix themselves after some driving. Good luck.