Stalling under load (bogging down)

09-08-2007, 08:14 AM
Ok. I just got the car knowing there was a problem. Ignition system seems fine, I did a throttle body clean & new gas in car. The thing bogs down soo much under load that u cant even take off in drive. The only thing that confuses me is if u slowly up the idle in neutral, to 3000?(no tach), then u can hammer the gas and rev it up with no bogging down. Iknow the o2 sensor is shot (steady at 0.5 volts). So is the o2 sensor used only at lower rpms? If not what else other then the o2 sensor am i gunna have to change? I was thinking fuel pump, but at high rpms its fine:S When i disconnect the o2 senor it acts just as described. By the way its a 94 Corolla. Thanks guys.

09-08-2007, 03:21 PM
Check for vacuum leaks -- this would cause bad MAP sensor readings such that the PCM will not know when the engine is under load.

A failed injector or harness possibly?

Bad spark plugs or wires.

Exhaust restriction, either in the muffler, the pipes, or the CAT(s).

The engine sensors are critical, but in different degrees -- the coolant temp sensor could also cause a similar issue, but it should cause the CEL to illuminate and/or store codes (have U checked for codes?).

* It's probably a better idea to disconnect the O2 sensor(s) than have it/them give false readings -- the PCM should compensate by running open loop code that should run the car fine.

09-08-2007, 05:34 PM
As SpinnerCee noted, take another look at those plugs and wires. Bogging under load is a primary symptom of a failure in that area. How old are the plugs and wires? If a '94 still had a distributor cap and rotor, you need to look at those also.

09-08-2007, 08:04 PM
Ignition seemed fine by looks no corrosion on cap or rotor plugs ok. I poured water on wires and cap, no arcing. I dont know how old they are since i just bought the car. Ohh and one more thing i forgot, when i first got it it did bog down but it was drive able i made it around the block twice, then it got worse and you coulnt take off in drive without it stalling.

09-08-2007, 08:07 PM
And with the o2 sensor disconnected the problem doesnt seem to change at all.

09-09-2007, 06:40 PM
Any smoke from the tailpipe?

In a "new" used car, the gasoline (and overall fuel system) condition is likely suspect, and may contain water/moisture -- gas goes stale over time so try to empty the tank by driving (not the best idea) or siphon (best way), then getting a fresh tank. If the fuel pump is not supplying sufficient volume or the fuel filter is dead/clogged), the engine will sputter.

The electronics are the engine's eyes and ears, so even simple things must be considered -- ie: the throttle position sensor on the throttle body can cause the issue you describe.

Simple things: I shouldn't have to say this, but a really dirty air filter (please say you changed it) or clogged airbox and ducts will also cause a bog.

09-09-2007, 09:51 PM
Like i said i ran the tank ALMOST empty put new gas in it, air filter i didnt change but its clean as a whitle. What i dont get is when i first got it, it bogged down; but after a drive around the block it just got so much worse:S
Well thanks for the advice so far, Matt

09-10-2007, 08:07 AM
You need to give more detailed info to diagnose this...

You keep saying "when I first got it" ? -- describe the problem with respect to the engine -- ie: when the engine is cold vs warmed up -- how much time does it take for things to change?

If the air filter is completely clean and never gets dirty, there could be a blockage before it -- tha air box should have two inlets -- one above and in front of the battery, and one litle known one next to the battery that opens in the wheel well. Try disconnecting the inlet tube at the throttle body, and test drive -- this will not hurt anything unless you drive through a sand storm.

Test the injectors and harness -- at idle, disconnect the electrical connector to each one at a time and notice the change in idle -- you have found a bad injector or wire if nothing happens when you disconnect the connector.

Test the MAP (manifold air pressure / vacuum) sensor -- it is found high on the firewall and will have a vacuum hose coming from the intake plenum attached to it -- the car should stall immediately if you pull the vacuum hose -- if not, the sensor or harness may be bad.

The Catalytic Converter can really only be tested with an exhaust back pressure test -- but it should be done because a bad one will certainly give you the "bananna in the tailpipe" symptom you describe. When CATs die, they clog. This relates to the O2 sensor because if the engine runs too rich, it will destroy the CAT.

09-10-2007, 07:51 PM
Ohh ok when i say when i first got it i meant the car i got the car and i knew it had the problem. I just didnt think it would take me this long to fix hahah. The problem occours all the time equally with no relationship to engine temperature.
The air ducting has nothing to do with it either, becuase I did a throttle body clean, and even with it all off the problem didnt change.
I checked the codes with a jumper wire and none exisisted.
I checked all the injectors, they all lowered idle when removed.
Ive disconnected the TPS, CTS, IAT, o2 and one other under the throttle body, wich i thought was the MAF sensor. All made the engine speed up accept unplugging the o2 sensor didnt seem to make a difference at all.
I can get my hands on a fuel pressure gauge, with a shrader valve, is there one on this car or not, i coulnt find it.
What confuses me even more: After work i disconnected the TPS and the thing ran perfect, no problems so i left it disconnected for now. Went out later in the evening, and the car was bogging down again with the TPS still disconnected!

Thanks for your help, Matt

09-18-2007, 07:37 PM
Ok more info, still have the problem!!! THe problem is now intermittant:S Well ive check fuel pressure(both when working right and the problem occouring) and is fine, i took the timing cover off and checked if the timing marks on the crank and cam lined up and they did. The coolant level might be going down, not sure, but could a intake gasket leak cause this maby? The only other thing i can think of is a partially clogged cat.

Any advice, Thanks, Matt

09-19-2007, 09:19 AM
TPS - Throttle Position switch -- pay attention here for a while...

Engine temperature (read by the CTS sensor) changes how/when the PCM applies or ignores various sensor inputs -- ie: until warmed up, the engine will ignore O2, IAT, and possibly TPS to run the fixed cold-start/warmup tune -- In your case, if the engine was cold when you first disconnected the TPS and the car ran fine until it warmed up, you should pay some attention to the TPS -- "warmed up" does not necessarily mean up to operating temp, so the closed loop code (using sensor feedback) is probably coming into play well before the engine is fully "hot" (maybe even before the thermostat opens @195 deg. F) -- this could explain the intermittency of the issue.

The TPS can be tested -- it has two (maybe three) electrical components -- an on/off idle switch, to tell the PCM when... you know -- and a variable resistor that mimicks throttle position (and possibly a WOT indicator as well). The Chiltons book has the procedure for testing it. Depending on what is wrong with the TPS a code and/or CEL may or may not be indicated. Did disconnecting the TPS give a CEL (check engine light)?

The CAT is also a likely culprit.

* I also want to add that at one time I have experimented with fixing several of the sensor values with different resistance values -- in particular the CTS (coolant temp sensor) -- If I substitute the warmed up [~195degF] sensor (resistance) value (~200 ohms) on a cold engine it will act like a car with a carb, hard to start, stalls until warmed up, etc... Doing the extreme opposite, using a cold engine value [~45degF] (~3200 ohms), the car will be the running cold-start, "rich" program even when warmed up -- this causes bogging under acceleration and a fast idle because the engine will be running the "choke" function, providing (too much) extra fuel and possibly ignition timing for a warmed up engine. What this may mean for you is that you should at least check the CTS -- if you disconnect it, the CEL will light, but the PCM will compensate by running a fixed value for the sensor, that should run the car well -- when this sensor fails, it may not totally disappear (read infintiy or zero ohms), instead it may just fail to respond properly or accurately to coolant temp changes the way it should. BTW, the CTS is independent from the dash gauge sender if you have one -- this means that a correct reading (or no reading) on your gauge does not indicate proper operation of the CTS. An indication that the CTS is reading "hot" (>200degF?) would be that the engine cooling fan would turn on (with A/C off), even when the engine is cold.

09-23-2007, 10:53 AM
I bakprobled the o2 sensor and it seemed fauly. It was a 2 wire and i had a 4 wire so i spliced it, knowing the other 2 wires are for the heater. Backprobing seemed to tell the o2 sensor was working, but the problem was still there. Brought the car to work, a guy has a snap on scan tool, no DTC's, but the o2 sensor was reading lean the whole time, and the ecu was in open loop. So i bought the right o2 sensor, plugged it in, when the car warmed up, it was reading lean,rich,lean,rich etc, and went into closed loop!:D Drove the car home fine(15 min drive), that night left home and 10min later thing bogged down and stalled, at that point i unplugged the TPS, and i made it home OK, it was acting up but not as bad. By then it was running ok, so i plugged it back in a left again, well i needed a tow truck lol. The car is at work now, when i disconnect the TPS the MIL light does come on. Im gunna hook up the scan tool again, see what it says, then cut out the cat, put a straight pipe in (for now). Disconnect the plugs from the ECU, do a contuniuty test on the o2 sensor wires with the o2 disconnected, then a load test on the wires(headlight). If none of that fixes the problem, ECU?

Well thank you, I really appretiate the time ur spending trying to help out,


09-25-2007, 05:51 PM
So Mon i go to work try to start it, nope, wont go. Disconnected fuel line, fuel yup. Checkd spark, nope. So i checked for codes, none, from scan tool readings, TPS, CTS and MAP all are working. So tested ignition coil by applying pos and neg to termianls and a sparplug to the end of the coil, works. The plug going to the Coil has a steady positive but the other wire is dead no neg or pos. Just finished pulling the ECU, no corrosion, then checked all the wires going to the coil & dist, for contiuity, none, wires arent shorting. Im gunna do a load test on those wires 2moro with a headlight.

So is there a common ignition problem with these cars?

You think the no-start is related to my previous problem??

Man, this is fun lol. Got this car for my GF, just bought a prelude for a winter beater i gotta fix up, restoring a charger and trying to keep my truck on the road lol.

Thanks to everone here that contribtes help, great fourms.

10-05-2007, 07:20 PM
Well i found the problem with a lot of testing. THE IGNIGTOR!! I thought they just went and thats it, but apparently not. Well, Ive got her runnin, driving fine for a couple hours definitly got it. Hopefully get another 5 years before the next problem. Thanks for all your help; Matt

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