4A-Fe Rough Idle At Warm Engine Temp

[awrhodes]

Greetings, I am having a problem with my 95 1.6L that I can't seem to figure out. I have searched many forums and tried many things that resolved others' similar problem with no luck. Basically, the car runs absolutely fine while driving along or for short distances. Once the engine temp gauge reaches the middle, at red lights or in traffic, the engine begins idling very rough and almost stalls. Once you're moving again and the temp cools, all is well. Here is what has been done so far. The fuel pump was replaced a few months ago due to a no-start issue. While troubleshooting that problem I swapped a few things and kept the originals, along with some other maintenance items which I have tried in solving this problem including: Distributor, Ignition Coil, Cap & Rotor, Plugs, TPS, Coolant Temp Sensor, IAC Valve. While trying to figure this out it did once throw a code for the air intake temp sensor, but my brother, a ten-year Toyota tech said he has never seen one go bad on this engine and doesn't believe it would cause this condition. I'd hate to throw another $40 part at the problem and I can't seem to find a salvage or donor part in my area. The condition is the same with this sensor plug in, or not. Thoughts? Also the condition is the same with the O2 sensor unplugged. It may be due for replacement but not sure if that would cause such behavior?

 

One other thing that might be worth mentioning is that when the fuel pump was replaced about 3 months ago (I gave up trying to figure out the problem and took it to the dealer), the technician showed me something very strange. The pump went bad because the one of the five pins on the connector had actually shorted and melted the pin out of place. It would intermittently cause me a problem until it finally gave out entirely. What's more, he pointed out that someone, at some point, for some reason, had cut and spliced the two power pins of the harness and put spade connectors on. Exactly why someone would do that we're not sure. There must have been some other problem with the fuel pump in the past, or perhaps these two problems are somehow linked? I checked the harness again and nothing indicates that the pump problem is reoccurring, just thought this information may be important to disclose.

 

One last thing I find interesting is that when I purchased the car about a year ago in Florida it didn't seem to run as warm as it does now. It's not overheating but I remember noticing that even in the dead heat of summer the temp gauge wouldn't even reach the middle point. The car was a one owner with 87K when I bought it, 103k now. I have no idea of the maint. history. I just flushed the coolant and it was pretty nasty but that didn't help.

 

This is such a great car but this problem which seemed to develop suddenly about a month ago is driving me crazy! If anyone has had a similar problem or suggestions, that would be greatly appreciated. As with most of us these days, money is tight, so trying to resolve this as inexpensively as possible :) Thanks in advance! -Alex

[altezzaclub]

So, is it OK at normal running temp when you first arrive at the lights? Is it just the extra 10 degrees of temperature from sitting without the fan running that makes it rough?

[awrhodes]

So, is it OK at normal running temp when you first arrive at the lights? Is it just the extra 10 degrees of temperature from sitting without the fan running that makes it rough?

 

Thank you for the reply. If I approach a light after moving for awhile it will be fine because the temp has cooled enough for the gauge to not reach the middle. If multiple lights, or stop and go traffic the temp will reach the middle and problem begins. It's like flipping a switch, once that gauge hits the middle it begins to idle rough. To recreate the problem in my driveway I just let it warm up to temp and lightly rev the engine, as it drops back down to idle the rear view mirror will vibrate and almost stall. I don't remember it getting to the middle of the gauge before, even if I let the car sit and idle for an extended period of time. The fan does kick on but it doesn't help the situation. From what I understand about thermostats they usually just get stuck open or closed, right? Or could it be possible that the thermostat is now opening a different temperature than before? Also wondering what the sensor is on the thermostat housing. I've replaced the coolant temp sensor (2-wire), but there's another sensor on the housing (1-wire). I'm not even sure if this is a cooling issue, there just seems to be a direct correlation between the engine temp and when the problem begins.

Edited April 1, 2012 by awrhodes

[LittleRedSpirit]

Its more likely a fuel or spark issue.

 

Try inspecting all your injector wires, coil wires, anything to do with ignition and spark. Maybe your coil is dodgy and has lost some of its fluid and now its not working right, I'm not sure really. With intermittent faults you have to be very patient and observant to find them. Try replicating the conditions and then when it happens, tool around with the wiring and see if you can make it improve.

 

If you shake your coil and it rattles then it may be in need of replacement.

 

I don't have a lot of solid ideas on this one, but start there.

 

It could well be the air or water temp sensors going bad, I have seen that type of air temp sensor go bad and it can cause what you describe. More likely the water temp one though. If the air temp sensor is broken it will either read hot or cold all the time. The faulty one I saw read -30 degrees C all the time and made for hard starting.

 

You should get the sensors from the wreckers, and just swap them and see.

Edited April 1, 2012 by LittleRedSpirit

[awrhodes]

 

It could well be the air or water temp sensors going bad, I have seen that type of air temp sensor go bad and it can cause what you describe. More likely the water temp one though. If the air temp sensor is broken it will either read hot or cold all the time. The faulty one I saw read -30 degrees C all the time and made for hard starting.

 

You should get the sensors from the wreckers, and just swap them and see.

 

I think I've ruled out ignition coil, I've tried two with the same result. Ignition wires seem okay. I've also tried two coolant temp sensors, with the same result. I'm trying to track down a salvage air temp sensor, or see if the local parts store will let me borrow one to test in the parking lot :)

[ke70dave]

mmm interesting one. thankyou for putting so much detail in your question! makes life much easier for us to attempt to help.

 

edit, i just re read your post...you have tried everything i suggested already...ive got nothing...

 

as for those two coolant sensors, i belive one is the temperature guage in the dash, the other one is the temperature sender for the ECU.

Edited April 1, 2012 by ke70dave

[awrhodes]

 

as for those two coolant sensors, i belive one is the temperature guage in the dash, the other one is the temperature sender for the ECU.

 

That's what I was thinking as well. When the one that I've replaced is disconnected, the gauge still functions so I'm assuming that is the more important ECU signal. Regarding the thermostat itself, am I correct that it will usually just get stuck open or closed, resulting in either running very cool, or running very hot?

[LittleRedSpirit]

Yes with regard to the thermostat sometimes they stay shut, sometimes open, sometimes halfway.

 

Its not going to cause a miss as it has little to do with the combustion event inside the motor that is going wrong.

 

Try and pressure test your cooling system asap, as you might have a slight BHG that is only a rpoblem when things get really hot. Do you run nice coolant or water in the system? Do you eve get bubbles in the coolant or a white residue under the oil cap?

[altezzaclub]

Take the thermostat out and try running the car without it, although if it is half-open when you take it out of a cold motor you have probably solved it.

 

Head gasket also crossed my mind, but that is usually accompanied by starting problems or losing water. Can you pull the plug leads off one at a time when its running rough and see if it is one cylinder only?? That would be a step forward, although it will probably die each time you pull one off....

 

Also- if you leave it idling and keep it running, does the fan hold the temp steady?? That would mean the cooling system can handle maximum heat output. -or take it for a run up some steep hills then let it idle at the top. The halfway mark temperature shouldn't be all that much of a problem to the motor if the gauge is reading correctly, but it it is only going to halfway at 95deg it could mean trouble.

Edited April 2, 2012 by altezzaclub

[awrhodes]

Yes with regard to the thermostat sometimes they stay shut, sometimes open, sometimes halfway.

 

Its not going to cause a miss as it has little to do with the combustion event inside the motor that is going wrong.

 

Try and pressure test your cooling system asap, as you might have a slight BHG that is only a rpoblem when things get really hot. Do you run nice coolant or water in the system? Do you eve get bubbles in the coolant or a white residue under the oil cap?

 

Well, I never flushed or changed the coolant until yesterday, I've only had the car less than a year and have only done routine oil and changed the plugs as maintenance so far. The car always ran so cool it never seemed like a priority. When I talked to my brother about this, he said Toyota factory coolant is red. What I drained out of there was a nasty deep purple/brown color that looked like it might have been red 15 years ago. I'm just running water in there now. I did notice some bubbles, almost foamy, so I flushed it out about 3 times with water until all the traces of the old coolant were gone. Then the only bubbles were from the air purging. I've never noticed a white residue under the oil cap. How would one pressure test a cooling system, or is that a job for a shop? Hypothetically if a thermostat were stuck halfway would that cause the engine to run hotter than usual, but not overheat? My [non-professional] theory is that it could be running hotter than it should, or used to, which could be sending bad information from the various temp sensors, sending the wrong air/fuel ratio, messing with the 02 sensor, etc causing a rough idle. Sounds good in my head anyway :) Hoping it's not a head gasket, I'm relatively mechanically inclined, but that's probably a little beyond my skills and tools (and budget!)

Edited April 2, 2012 by awrhodes

[awrhodes]

 

Can you pull the plug leads off one at a time when its running rough and see if it is one cylinder only?? That would be a step forward, although it will probably die each time you pull one off....

 

 

I could certainly try that. I pulled them off one at a time when it was running normal and no particular cylinder seemed to be any worse than the others. I didn't think to try it while it's running rough, it probably will die. I can also try your advise on pulling the thermostat.

[awrhodes]

 

Also- if you leave it idling and keep it running, does the fan hold the temp steady?? That would mean the cooling system can handle maximum heat output. -or take it for a run up some steep hills then let it idle at the top. The halfway mark temperature shouldn't be all that much of a problem to the motor if the gauge is reading correctly, but it it is only going to halfway at 95deg it could mean trouble.

 

Yes, the fan does hold the temp steady at the middle of the gauge. I don't drive the car much since this started happening. When I do, I keep it idling by holding the gas a little (a bit tricky on hills using the clutch, gas, brake, and handbrake!), but I've never seen the needle go above halfway.

Edited April 2, 2012 by awrhodes

[awrhodes]

 

but it it is only going to halfway at 95deg it could mean trouble.

 

Do you mean if it is going to halfway quickly it could be a more serious problem? From a cold start, it will climb to the middle in about ten minutes at idle, then the fans will hold it there (cycle on/off), but it will run rough.

Edited April 2, 2012 by awrhodes

[awrhodes]

Ok, so I got curious as to why you would ask if there were bubbles in the coolant, so I quickly googled "foamy coolant". I'm seeing mixed information, but I'm not sure I like what I'm reading! I already had a friend take it to be disposed but now I'm wondering if I should have kept it. I also should have paid more attention to what kind of bubbles and foam, I just thought to myself, "hey this is kind of foamy." Shows you what I know! Apparently this is an indication of a BHG and I saw something about test kits to check for gases and so on. Maybe it was just really old and nasty, I'm thinking positive here. I also just checked my oil and it is at the halfway mark. I change my oil every 3k and it's right at the 3k mark since I last changed it last. It's not milky or white or anything, but I don't leave behind drops of oil so it must have gone somewhere. So since I've already disposed of the old coolant, if there is a BHG will the bubbles/foam reappear relatively soon? Could I have a minor leak that's not even related to this current problem? Man, it's a 7th gen Corolla with just over 100k, I shouldn't be having these problems! (but I wasn't responsible for the first 90k, so who knows)

 

Considering I'm practically broke at the moment, I think this will be my plan of attack. Please feel free to suggest anything else. 1.) Try to track down a salvage or borrow an air temp sensor since it did randomly throw that code once. Maybe this will make the ECU happy and we'll have a fairy tail ending. 2.) Pull out the thermostat while the engine is cold and see if I can tell if it's stuck in the middle. If not obvious, run the car without the thermostat to determine if it is faulty. If either are the case, go to Toyota and get an OEM thermostat & cross fingers 3.) Give up the DIY, and go get a coolant pressure and compression test, or general professional diagnosis whenever I can afford to and hope I'm not looking at a major repair.

 

If there's anything else I can cheaply try, I'm all ears. Thanks everyone for your input.

Edited April 2, 2012 by awrhodes

[LittleRedSpirit]

Any radiator shop will pressure test your cooling system for free, just drive down there and ask them to, as you have a temperature issue that might mean you need some work. Its jst what they do. Or any mechanic can do it. Make sure you do it while its running rough.

 

A blown head gasket can happen in multiple ways. You can leak water into combustion, you can leak oil into water or water into oil.

 

If you leak water into the combustion chamber then you will notice it go missing. You might also get bubbles in the coolant or a foam.

 

If you get water in your oil you will have a leak from a water gallery to an oil gallery. If you have excess oil consumption you either have worn rings or stem seals or are losing oil into the combustion chamber which is not likely through a bhg as the water is between the cylinder and the oil in an a series from memory in most places.

 

.5 litres over 3000klm isnt terminal oil use, itd be nice if it were lower but it all depends who serviced it and how often.

 

All this thermostat stuff sounds unlikely, and anyhow the car will be able to compensate for hot water or air temperatures thanks to its fuel trim tables inherent in the ecu. the only thing that can foul that up is faulty temp sensors. Its possible that you have both a faulty gauge and ecu water temp sensor. Might be worth fitting an after-market temp gauge so you can see how hot the thermostat is running the motor and what sort of temperature its really at.

 

So the plan of action is, make it run rough and at that time rev it up and look for bubbles in the coolant. I think it will run on 2 cylinders, just, so do the unplug thing and see if its a problem with one cylinder or all 4. Then go get a pressure test at the local radiator shop.