Engine lope at idle

I have a 1999 Camry 4Cyl with right at 180,000 miles on it. I faithfully make sure the scheduled maintenance is done per my shop manual specifications.
I'm amazed how this car still starts, runs and rides like a new one.

The car starts right up when cold and runs smooth as a top and soon it is warmed up to normal operating temp after just a few minutes of driving.

Approximately three or four months ago, when the car was at operating temp, I stopped to get gas. When I got back in the car and started the engine, I was putting on my seat belt when I felt and heard the engine loping. I looked at the tachometer and noticed the tach needle loping up and down between the six and eight hundred RPM marks on the tach. It did this for only fifteen seconds or so and finally settled down on the six hundred RPM mark and held steady. I dropped the car in gear and drove off and when I arrived back home I noticed the needle was still holding steady on the six hundred RPM mark with no loping present.

I wrote this off as just a quirk of some kind, because it had not happened prior and did not happen again until just yesterday, when again it did the same exact thing. With a warm engine and at start up the tach would slowly wobble between six and eight hundred RPM for 15 or 20 seconds and then suddenly stop doing this. The engine would never completely die on me, and when I would put the car in gear I could drive off with no problems and I would experience no more tach lope all the way home.

In a few months my timing belt is due to be changed as well as my fuel and air filters. None of these are actually overdue to be changed. Two years ago I replace the spark plugs and plug wires with the best you can buy.

My oil and filters are changed faithfully and the engine leaks zero oil and burns less than half a quart between oil changes.

Being very conscious of my cars performance, I want to be sure if this rare periodic loping that has happened only twice is possibly a symptom of something I need to be concerned about. Is it possibly just an air or fuel filter that just needs to be replaced? Or, symptoms of something more serious like a fuel pump that is on its way out? Or, is it something as simple as just bad gas that I can just ignore.

I hate to go throwing money at things needlessly if it is not necessary.

Has anyone else experienced this loping problem that might have some suggestions?

Above post was edited by me to reflect actual rpm.

With respect to your problem with the unstable idle, I would suggest ignoring it since it is infrequent and not really a serious issue. If and when it becomes more common, then it will be easier to troubleshoot. Right now, you would be only guessing. Anyone else with similar symptoms may have a totally different cause and you would still be guessing.

If you want to have something to think about, many brands of spark plug wires and plugs do not work well in that engine. DENSO or NGK plugs and plug wires are the only ones which are reliable from my experience.

It is definitely not an air or fuel filter.

With respect to your problem with the unstable idle, I would suggest ignoring it since it is infrequent and not really a serious issue. If and when it becomes more common, then it will be easier to troubleshoot. Right now, you would be only guessing. Anyone else with similar symptoms may have a totally different cause and you would still be guessing.

If you want to have something to think about, many brands of spark plug wires and plugs do not work well in that engine. DENSO or NGK plugs and plug wires are the only ones which are reliable from my experience.

It is definitely not an air or fuel filter.

Thanks Brian for your tips! The replacement plugs and wires I installed were NGK.

I would follow Brian's advice and not do anything unless the symptoms get more frequent. The one cheap and easy thing you can do now since this occurred after getting gas, would be to pour a couple of bottles of gas line antifreze in to the tank. It's possible you got some water in the tank along with the gas. These things do work at removing water in the tank.

Mike

I have had similar idle issues with my Camry 4-cyl (1996) which is very similar to yours. This unstable idle only happens once in a while and has never gotten worse. I have never sorted it out and don't intend to unless it begins to affect driveability.

If you get the urge, check your rubber hoses everywhere and replace any that are loose on the nipple they attach to, or are cracked or suspect in any way. It is a cheap way to forestall minor driveability issues and Check Engine lights. FYI, there are hoses under your car near the gas tank/charcoal canister.

Also, mysterious problems can result from a dirty EGR valve. They are able to be cleaned. It sits above the intake plenum hear the throttle body.

Another potential issue may be the PCV valve is plugged. They need to be changed periodically, particularly in your engine which has a ton of blow-by.

I would follow Brian's advice and not do anything unless the symptoms get more frequent. The one cheap and easy thing you can do now since this occurred after getting gas, would be to pour a couple of bottles of gas line antifreze in to the tank. It's possible you got some water in the tank along with the gas. These things do work at removing water in the tank.

Mike

Thanks Mike for the tip. I will do that.

I have had similar idle issues with my Camry 4-cyl (1996) which is very similar to yours. This unstable idle only happens once in a while and has never gotten worse. I have never sorted it out and don't intend to unless it begins to affect driveability.

If you get the urge, check your rubber hoses everywhere and replace any that are loose on the nipple they attach to, or are cracked or suspect in any way. It is a cheap way to forestall minor driveability issues and Check Engine lights. FYI, there are hoses under your car near the gas tank/charcoal canister.

Also, mysterious problems can result from a dirty EGR valve. They are able to be cleaned. It sits above the intake plenum hear the throttle body.

Another potential issue may be the PCV valve is plugged. They need to be changed periodically, particularly in your engine which has a ton of blow-by.

Thanks Brian for the advice. It's nice to communicate with guys like you and Mike who seem to know what they are talking about.
So far I don't have any check engine lights coming on. Should I also check all the vacuum lines also attached to the top of the engine?
Does the EGR valve screw into the throttle body?, or is it spliced within a hose?

The EGR valve is attached to the side of the intake plenum (two studs), and connected with hoses, if I remember correctly. Check all the lines you can find. They are probably pretty much ok, but finding one bad one or bad connection can be worth it. You won't get a check engine light for a bad hose unless it is associated with an emissions control system. Hoses that affect your fuel/air mixture are the ones which would probably affect your idle in the way you describe. Any intermittent vacuum leaks into the intake manifold or air plenum may make your idle strange.

There is also a filter in the EGR vacuum modulator (next to the EGR valve) which you can clean with compressed air or other means. If you remove the filter, install it with the coarser surface facing outward.