93 V-6 Low speed engine stumble

[DSwarthout]

I recently bought a 93 Camry LE wagon with the V-6 engine. Although it has high mileage (>150 K miles) the body is perfect. The car performs very well, turns in 24 mpg hwy, and exhibits no missing or hesitation at all under load. But at idle or with just a little pressure on the accelerator pedal, it stumbles or misses. It began with just an ocassional stumble but it's getting worse daily.

My mechanic is convinced it's the throttle position sensor. He's getting some resistance when he should get none and he says some contacts inside are corroded. He didn't go ahead and replace my tps because I couldn't leave my car there for the weekend but we're planning on doing that next week.

Being new to such electronic controls myself, I thought I'd post a question in here and see if anyone has had a similar symtom, and if so, whether replacing the tps solved it.

Thanks,
Dave

[Toysrme]

WoW man! You're patient LoL!
By that I mean you really have to not work a great condition 3vz-fe to get to 24mpg hahahaha! That's well over 400m a tank!

Aaaaaanyways, I highly doubt the TPS is the cause of it. The TPS signal is only used to trip the ECU from closed loop mode (reading the o2 sensor for economy/emissions), To open loop mode (Forgetting all of that and use stored settings for performance).
When it changes, it's a seemless change. If you want to know what the change feels like, romp down on the gas to about 70%, then push it all the way down. See... It's seemless.

All of that being said... Look for the common things first.

Vacuum/intake leaks (broken/disconnected hoses), Fuel problems (clogged filter ect) or bad spark (bad plugs, or incorrect ignition timing).
Check them in that order.

[DSwarthout]

Thanks for the compliment, and the feedback, Toysrme. Yeah, I don't run it hard - especially cause it's still new to me and I'm not familiar with its quirks yet.

Just as I was driving today I began to rethink that TPS theory because not only is the engine stumble getting worse, I find that it is no longer dependent on the accelerator postion now. It's happening at speed.

So you think it isn't the TPS but fuel or something ingition related? Ok, that sounds logical. In you post you stated look for "Fuel problems (clogged filter ect)." Is there a part named "ect" or did you mean "etc." ? (Sorry for the confusion.) Another person suggested fuel filter problems as well. I'll check that out then look at spark plug wires and other ignition stuff. (BTW, is there a resistance value that you know that might be used to evaluate the wires? I recall the figure of 7,000 ohms per foot somewhere in this forum. Is that correct?)

One more point - or clarification if you will. You also said check the timing. If the timing were out of adjustment, wouldn't it be more likely that the car would perform badly all the time? I'm getting great gas mileage and when I put the pedal down to the floor, it gets up and goes! In general, the timing would need to be ok for that to happen, don't you agree?

Anyway, any more of your thoughts?

Thanks,
Dave

[ArmyofOne]

what part of alaska are you in? i lived in Anchorage (near the AFB) my entire life.

the fuel filter or pump could definately be a problem.

also, remeber, if there is the slightst bit of water in the gas lines, at the temps you guys have right now (i woudl imagine minues 20 or so) they water wil likely be frozen. could be a lot of things though:

Bad ECU (probably not the case)
Fuel Filter
Vaccuum leak
Dirty Throttle body
Dirty MAF (this could be the case in AK, the roads are horrible and in the spring...oh my god..the slush and mud!!)
clogged air filter (this is what i would check first
Spark plugs
wires
coil
distributor
distibutor cap
Fuel pump
Compression issues (piston rings/valve seals, one means engine tear down and one means head tear down)
and lastly, we come to tranny issues. there are many thinsg that can cause this, start with the cheapest and work your way up.

here is an easy way top diagnose the ignition system and rule it out as a possibility:

start the engine and take off the spark pulg wires starting with the first one on the rigth side front. do them one at a time. do it quickly to get it out of the range of sparking distance (a few inches) from the valve cover. hold it up and see if the engine changes the way it runs. if it doesnt, thats your problem, but put the wire near the valve cover and see if it arcs a spark to the cover (or other metal part) DO NOT STICK YOU FINGER IN THE WIRE/NEAR IT WHILE YOU ARE DOING THIS!! YOU WILL BE ELECTROCUTED!! HOLD IT BY THE TOP PART THAT YOU HAVE TO GRAP TO REMOVE IT!!. if the wire sparks, the problem is the plug, if not, it is the wire or the distributor.



when reassembling the intake, you may very well find that you have fixed the issue.
you will most likely have to remove the upper intake manifold (that part i described above) to perform the spark check.

[DSwarthout]

Thanks ArmyofOne,

I'm in Homer. We don't have the severe temps that Anchorage gets (as you probably know) yet this problem is hard to work on because even here it ain't exactly warm outside. That's why I've been using the forums and not doing the necessary work outdoors on my car. <g>

I think the fuel filter is a likely suspect. But getting at it is gonna require contortions. You know, I ran two cans of Seafoam through the tank to clean the injectors and I'm wondering now if I might have loosened up a lot of crud from somewhere that clogged up the fuel delivery system. I won't be able to check this till the weekend though. In the meantime, I'll dump a can of Heet into the tank and see if that won't help. Then it's time to check the ignition system.

As I said in the post to Toysrme, this thing is getting worse all the time. It doesn't seem sensible to expect the throttle position sensor to degrade so fast. Other posts suggest that the tps wouldn't cause the kind of stumble or miss I'm seeing anyway - but I don't really have a clue myself. I'm new to cars with ECMs and AFMs and EGRs, etc. Used to have a 90 Subaru Loyale (aka: The Goat) - the best Alaska car ever built. Able to climb trees with good studded snow tires on!

Dave

[Toysrme]

The electrical gismo's aint too complicated to understand, and don't cause problems haf as often as the good old mechanical parts, so don't pretend to be lost in the early world of EFI!

Easyest way to take the fuel filter out is to take out the stock air box and if you have to, the EVAP system by that.



^^^
I highly doubt seafoam "knocked" crud free. It's mainly a few potent petrolium based solvents. It eats things away.

Just be sure after you change the filter, if it's not running better to check for vacuum leaks. I don't think there is a rubber intake hose on any Toyota car over 10 years old not cracked hah!

EFI 101:
If there is a crack, then air comes in through it. This is bad because the ECU needs to know exactly how much air is flowing through the system to decide how much fuel to squirt(and ignition timing a lil bit). If it's off... Then they normally lean out and run like crap.