1999 Toyota Camry

Engine Performance problem
1999 Toyota Camry 4 cyl Front Wheel Drive Automatic 70000 miles

I have a 1999 Toyota Camry 4 cyl with 70,000 miles on it. On really hot days when I stop at a light, the idle can suddenly drop and bounce suddenly. During stop and go driving in summer I have never seen the temp gauge go beyond half way. On a hot day (above 95 deg) the temp gauge can hit the half way mark within a mile or two of in town driving. Soon after it reaches half way mark the idle speed at a light will usually drop to 600 RPM. Usually after the first time I noticed the rpm at 600 at a stop, at anytime while stopped the idle can suddenly drop to 400 and bounce back up to 1000. It feels like the engine is about to quit and the idle is real rough. At a stop when this occurs, I shift into neutral or park and accelerate slightly to keep the rpms above 600 rpm. If I use the conditioner the idle problem will show up sooner. During the idle problem the check engine light never comes on. Also after the idle problem first appears while driving at a stop, at any time while driving I can lose power during acceleration. It kind of has symptoms of vapor lock but the fuel filter under the hood is always cool enough to touch. I have taken it to shops and they checked the computer, fuel pressure, etc. And couldn't find anything wrong. This problem never occurs in winter or when the temp gauge is below the half way mark. I had the EGR replaced, new plugs, cleaned the throttle body and had the injectors flushed. This didn't solve the problem.
This has been happening the last three summers. Any ideas what could be causing the problem and how to resolve it.
June 25, 2008.

Hi dezrat1,

Did you clean the IAC and check if its bypass hoses and system are clogged?

Coolant passes under the IAC to provide a signal to control the opening of the air flow valve.

Other possible areas to check are the ECT, IAT, MAP and cooling system, ie, fans, radiator coolants.

Jun 27, 2008.
I noticed the fans were not coming on when the engine heated up. The fans would come on only when I turned on the air conditioner. I replaced the radiator cooling fan switch and ECT. The fans still would not come on with out the air conditioner on. Well I drove the car on a cool rainy day and when it got to operating the temperature the idle again would shake and idle speed bounce as before and if I turned the air conditioner on it the idle would drop to 400 and shake erratically and almost die. So after some more Internet research I found the 4 cly has no maf sensor. I pulled the hose off the throttle body and spray several 3-second bursts down the IAC hole. I had to use a piece of aquarium tubing to extend the spray tube to get down the hole. I let it soak about 30 minutes and reconnected the hose and started the engine. It was sluggish for the first few seconds and I drove it around the block and repeated the process. The idle really smoothed out and now I can use the air conditioner. Before I could barely make it to work and back before the idle problem would resurface and if I had the air on I couldn't make it home without the idle problem resurfacing. After cleaning the IAC the problem has never reappeared even on hot days. I can keep the air on the all the home from work without any idle problem. The idle is much smoother. I still haven't resolved the radiator fan problem. I replaced all the fan relays and the main engine relay and the fans still will not come on. I later learned how to test them and that tested fine (old & new ones).
I disconnected the wire from the radiator cooling fan switch and turned the key to ON position and fan still would not run. So far I keep the air conditioner on while driving and this keeps the fans on. Still working on fan problem. Any suggestions how to diagnose fan problem?

Jul 17, 2008.
Hi dezrat1,

If removing the fan switch wire did not start the fans, you need to check the fan switch wire for grounding, it is shorted to body.

If not, the you need to check the relay terminals.

Jul 18, 2008.