My 1999 Camry with 200 K + miles still works pretty well. However
over the last several months I've had a problem with engine power loss when the engine is warmed up. The tricky thing here is this only happens when the car has been off for 10 to 30 mins. Now that the weather is colder the problem is amplified. When this problem happened in warmer weather I could pull over & let the engine idle for 5 min. The power would be normal after this 5 min idling.
This only happens when the engine is fully warmed up.
My mechanic has replaced transmission fluid, replaced the idle motor, & some temp sensor, most recently the radiator was flushed and new thermostate installed.

It seems to be related to engine internal temp vs external temp. My mechanic mentioned sensor(s) related to this, not sure he got the right one(s)

We can drive it with no problem 300 miles at a shot. But if you do a pit stop, and turn the engine off, you got a problem. The engine isn't cold, but not actually running hot thermostate registers warm, outside temp is now 30to 40 F range & problem is bad. Rough running, low power.

 

V6 or 4 cylinder?

If the engine always runs rough after restart and is fine after 5 minutes find a mechanic that can access the engine computer via the ODBII port and output real time data for the sensors, air/fuel ratio, etc.

With equipment installed on car, restart car and compare data output when running rough to when back to running OK.

This will allow the mechanic to determine if the problem is fuel or ign related to narrow down the search and find the problem.

The mechanic should also check fuel pressure when engine running normal and after rough running restart.

Does the engine always run rough after restart regardless of time the engine was off, such as a quick shut off then restart?

 

Thanks for the reply. Sorry I didn't mention it is 4 cylinder, autotransmission.
If I shut car off for just a few minutes it will start right back up. Sometimes I can leave it for 10 min or longer and it will start up just fine, it seems to depend on the outdoor temp. Now with colder weather this powerloss phenomena is more pronounced.

This evening the ambient outdoor temp was 40-45 F we
drove for 10-15 min then left the car off for 60 min,
drive on for 5 min,
off for 5 min,
then drive on for 2 min flat terrain normal power,
then off for 20 min,
on drive for 2 min (again flat terrain,normal power)
then off for 3-5 min,
on drive for 10 min, when attempting uphill power was low & erratic, pulled over with engine running for 5 min idling, power came back and was able to drive up hill.

 

Thus when going up hill the engine had no power, has this happened before?

When the engine experiences loss of power does the check engine light come on?

Just a guess but would look at the crank and cam ign sensors (perhaps the mechanic changed one of these). A mechanic can check these with an ohm meter.

Or a fuel pressure issue such as fuel pump/pressure regulator.

If a shop can repeat the problem they should be able to tell via their equipment if the problem is ign related or fuel.

You might find another mechanic.

 

Joey P,

I appreciate you taking an interest in this problem of mine. Engine Check light, well good quest. We've been running the car just fine with the engine check light on for about 7-8 years or more, maybe 100mi + .
How you may ask, to pass inspection my mechanic does some elaborate magical fussing, he is only then able to clear light & pass inspc. Within a month the light is back on. Been doing this for almost 10years. Brought it to a dealer once. Once, they were just jackasses, charged $75 to put up on lift, then decided they should look at bulletines for '99 Camrys, discovered that O2 sensor chip was bad (it was eating O2 sensors). Toyota factory issue, still charged me & gave me run around.
This particular power loss problem has been going on for about 6-8 months. Mech changed some things, idle motor, temp sensor. He has connected it to computer for diagnostics. Problem appeared solved for 1-2 mons, over the summer it wasn't much of and issue. Now with colder weather it is more pronounced. It seems difficult to replicate without getting the engining cooling off just the right amount. Mech told me it is likely a gas/air mix issue as engine is hunting for it's true temp. However it appears engine thinks it's colder than it is & makes richer mix. My wife tries giving it more gas to address the low power & engine stalls out. I've tried more gas in these situations & power loss is increased, I've not stalled it out.
Your suggestions are very helpful, I'm bringing it back to mech for overnite exam. He will review your suggestions & look crank & cam ingnit sensors along with fuel.
Thanks loads, I hope to get at least 30K more out of this car.