87 Camry, Cold—fine, Warm—runs poor

[87cam]

I need my 87 Camry to get me through 1.5 more years of school, please help. My 87 has plenty of little problems but was working fine until last week. Now about a minute or two after start up, just when the water temp is starting to register, the car begins running really rough. I have taken it to a couple of mechanics both of which did very little diagnosis and wanted to charge a lot for a simple tune up. Because the car runs normal during cold operation, I do not think that a simple tune up is my problem.

After reading a suggestion on this sight I have changed the O2 sensor but that has not solved the problem. Because I do not know how the computer interacts with the components, I am having a hard time determining what it might be. I think it could be a problem with sensors, vacuum pressure, fuel delivery, ect. Some of the respondents on this sight seem to know their stuff. Any suggestions would be appreciated.

Car’s symptoms:

• Normal operation when cold
• Runs rough when water temp starts to register
• When warm, idles ok in neutral but not in drive (automatic)
• Won’t accelerate properly
• Bucks and sputters when driving down the road

[Mike Gerber]

My next thought (the O2 sensor was a good first one) would be to check the coolant temp sensor. It may be defective causing an overly rich mixture all the time. This will make the car run normally when it is cold, as a rich mixture is needed for a cold engine. Once the engine is warm, this overly rich mixture is not needed. A much leaner mixture is needed for a warm engine. The coolant temp sensor tells the computer what the engine temperature is and the computer then richens or leans the mixture accordingly through the length of time the fuel injectors pulse. A defective coolant temp sensor may also cause a noticable drop in fuel economy. You will need a simple manual and a digital volt/ohmeter to check the coolant temp sensor. If you are standing in front of the car, the coolant temp sensor is located just to the right (driver's side) on the engine block, in a metal coolant passage. You will see 2 plastic connectors there. One brown and one green. The coolant temp sensor is under the green one. (The brown one is your cold start time switch.) There will be a wire lock around the connector. You must pull back this wire lock to both sides of the conector (I use a tiny flat head screwdriver) and hold them to the outside of the connector (I use toothpicks for this) before pulling the connector off. Sorry I dont have the specs for testing the sensor, but any manual will have them.

If the coolant temp sensor checks out normal, my next thought would be to have someone put a gage on the fuel rail and check out the fuel pressure. The fuel pump may be getting weak.

Good luck.

Mike

[Un-Mechanic]

Originally Posted by Mike Gerber

My next thought (the O2 sensor was a good first one) would be to check the coolant temp sensor. It may be defective causing an overly rich mixture all the time. This will make the car run normally when it is cold, as a rich mixture is needed for a cold engine. Once the engine is warm, this overly rich mixture is not needed. A much leaner mixture is needed for a warm engine. The coolant temp sensor tells the computer what the engine temperature is and the computer then richens or leans the mixture accordingly through the length of time the fuel injectors pulse. A defective coolant temp sensor may also cause a noticable drop in fuel economy. You will need a simple manual and a digital volt/ohmeter to check the coolant temp sensor. If you are standing in front of the car, the coolant temp sensor is located just to the right (driver's side) on the engine block, in a metal coolant passage. You will see 2 plastic connectors there. One brown and one green. The coolant temp sensor is under the green one. (The brown one is your cold start time switch.) There will be a wire lock around the connector. You must pull back this wire lock to both sides of the conector (I use a tiny flat head screwdriver) and hold them to the outside of the connector (I use toothpicks for this) before pulling the connector off. Sorry I dont have the specs for testing the sensor, but any manual will have them.

If the coolant temp sensor checks out normal, my next thought would be to have someone put a gage on the fuel rail and check out the fuel pressure. The fuel pump may be getting weak.

Good luck.

Mike

Hi Mike I got a quick question for ya.

You describe the brown connector as the cold start timing switch. I have a 94 Camry with a brown connector but the Toyota computer says I don't have a cold start timing switch on that model. It has a brown connector and only one wire running to it....sound like the cold start switch to you or something else on that year of camry?

[Mike Gerber]

Un-Mechanic,

I think you are correct in stating that the 94 does not have a cold start time switch. I think they were only used on the generation 1 (83-86) and on early generation 2's (but I am not sure whether all the generation 2's had them or not). They were gone on the generation 3. I see the problem you are having from your other post. I think the generation 3 gets it temperature signal to richen up the mixture for a cold start directly from the coolant temp sensor, which your mechanic already has changed out. That would have been my thought too with reference to your problem so I didn't post anything there; I didn't have anything more to add. It is possible that the replacement part is also defective or that there is a wiring problem between the sensor and the ecu. You can check the coolant temp sensor as described in my earlier post. You can also try checking the continuity of the wiring between the sensor and the ecu. These should be pretty simple tests for an experienced tech.

Good luck.

Mike