Engine surging.

Sounds like a fuel issue...Try running some fuel system cleaner thru the fuel tank...After setting a while fuel turns into varnish...Nasty stuff...

I forgot to mention, I ran fuel system cleaner through, and changed both the fuel & air filters. I drive it about 240 miles a week with no other problems except this annoying surge, which unfortunately seems to be getting worse, happening more frequently.

Could be a weak fuel pump or fuel pressure regulator if so equipped...

Thanx for your suggestion, but after careful thought and consulting a mechanic, we concluded this probably isn't fuel related. Car accelerates cleanly, and holds steady on heavy load &/or incline. The only time the problem occurs is while coasting. I just replaced the O2 sensor with little improvement. EGR & PCV valves have been ruled out. Is there an idle sensor, or such a thing as a deceleration sensor or solenoid? A shop wants to charge over $100, and won't guarantee they'll even find the problem!

Have you checked for vacuum leaks? They are a common cause for surging...

I just took a look a few minutes ago. Vacuum lines appear almost new. Checked connections, but there's dozens of 'em! I need to check again tomorrow when it's light & not so cold, with the engine running, and a can of carb clean in hand. I did discover the car has CA emissions, and a "downstream" O2 sensor I missed earlier. Why do CA cars have 2 sensors, and if the "upstream" sensor is new, could the surge, (only while coasting between 900-1500 rpms) be caused by the 2nd sensor? EGR valve is basically for recirculating exhaust gas on start up only , isn't it? Can it cause fluctuations after warm up too? What does the MAF sensor control? And why would a coolant temp. sensor cause surging?! Sorry, I've been researching and have come up with lots of questions, but no real answers...

O2 sensor may be it...EGR works continously to cut down on NOx by lowering combustion temp...Sometimes they need cleaned or replaced...MAF is the mass air flow sensor...Located just before the air cleaner on the intake tube...It measures incoming air volume so the computer can adjust air/fuel mixture...How about the throttle position sensor? I had an F150 that had a bad one the had a sticky spot and would surge on either side of the sticky spot...Just happened to be at 55mph...

I thot about the TPS, and may be over thinking things, but the surging happens at pretty much any speed between 20-50 mph @ low to mid range rpms, and only while coasting. Touch the throttle or even the brake, and the surging stops. Lately, I've begun to notice a VERY faint miss @ hiway speeds while maintaining speed, but it's never consistant, nor strong enough to overly concern me... (except, I did replace all those obvious parts already...hmmm...)

By the way... Thank you for taking the time to help out! I appreciate it!

I know this sounds crazy, but it sounds like no heated coolant is passing thru your iacv (idle air control valve), could be air an bubble in your cooling system, plugged iacv coolant hose, (by the thermostat housing is a small coolant hose that twists and turns, and goes under the throttle body), if this small hose gets plugged, rust, debris, or old radiator stopleak, or even an air bubble from filling a cold radiator wrong), your iacv thinks the engine is cold, but the rest of your engine knows its warm, the engine temp sensor, cold start injector, water temp sensor, all tell the computer one thing, the iacv tells it another, and tries to speed up the idle because the cold engine requires more fuel, point being the computer is trying to compensate for something. this is why the brakes, idle, coolant, fuel all seem sorta connected to, but not the reason for, your problem. 1 check radiator for reduced flow(plugged, or restricted), 2 see if an air bubble is in the cooling system, behind the thermostat(remove cap, run motor till thermostat opens, top off coolant) 3 check to see if iacv hose is blocked, it twists and turns and is way smaller then other coolant lines, it can be clogged, 4 if all this helps your iacv works, but was not working because the heat it needed to close was insufficient, in my case replacing my radiator was the fix, when I started looking at this problem you could not have convinced me the radiators restricted flow was my problem and my solution was so simple. good luck oh yeah the only thing that concerns me was on my truck the surging was when I applied the brakes, for you it stopped with brake application so im concerned our issues may differ, good luck and please let us know what works for you so we can get better performance for us too.

I am not sure how old this post is but i too have a 1989 Toyota Camry i have the exact same surging issue. But i come with your solution... i have changed cap, rotor, spark plugs, wires, coil pack, pcv valve, and i have checked pressure of all cylinders as well as fuel pressure all in one and individually at each injector. I have replaced the fuel filter and checked and or replaced every sensor on this car.... Now why i am telling you is for this simple reason of what i have not cleaned or changed... 1 Is the EGR Valve mine well lets just say 29 years and not one cleaning...so with that and the combined issue with a sticky throttle i have narrowed down the search. My problem as well as i hope solves your problem too is that darn purge canister replace that and your problem should disappear. If it does not then back trace your steps or problem solve....what i mean is start your car let it warm up to temperature and one by one unplug a sensor if you notice the engine die, or a drop or spike in rpms thats not your issue. If you get to say the tps like i did and unplug it and notice nothing change, replace the sensor but like i said my problem was a sticky throttle a plugged egr and a purge canister that went 29 years purging on. Hope this helped. good luck

I wish I knew how this came out, I have the same RPM rising and falling on my 3.0 Toyota Highlander.

I have the same issue with a 2009 corrola. Surges between 15-45mph and stops surging with a press of gas pedal. Really only happens when I’m trying to coast the car.

I have the something only it's a 92 geo prizm and it surges up and down the only difference is mine is a high idle then you press the gas petal a bit starts to sarge even worse press the pedal more about maybe a quarter or so it stops been told it's the map sensor I've replace it several times and checked for vaccum leaks not one. Can't find out what wrong.

Same issue on a 2017 Camry SE. The tachometer shows no change, however; but the engine suddenly sounds like it is surging (no difference in acceleration, fortunately) and calms after a few seconds.

I think Daniel should go back to selling shoes and not advise people with his odd automotive remedies. I do not have an answer, but sure as hell advise you people with the problem not to do too much trial and error as it could be expensive if not time consuming. Daniel I think your forte is more in line with shoe repair and not automotive repair!

same here with my 91 camry cant figure out what is wrong with it i need help bad, fyi toyotas or atleast my car does not have and idle air control valve

Rpm in my Camry 2000 fluctuates when I press the brake pedal and leave the car in Drive on a traffic light. Still troubleshooting the problem but I’ll mention what I have done so far. I cleaned the throttle body and iacv and the car ran a lot smoother but the problem didn’t go. Plugs are newish and I got new coil packs a few months ago. Fuel filter is new too. Although the car was smoother after throttle cleaning I could note some hesitation during hard acceleration. I checked all the vacuum pipes and found one of the vacuum entry point to be clogged with oil or something. I had recently cleaned it so it should not have been dirty at all. Sprayed some carb cleaner in that point while engine running to clear out lines and the acceleration was back to normal again with no hesitation or missing. This was hose coming from the charcoal canister. Opened it all up, cleaned the canister with water and made sure air was flowing freely through the 2 exits. Changed the vacuum pipes. The purge solenoid is located next (under) to the coolant temperature sensor (on the flange) so the solenoid works with the temperature of the vehicle. It ran good again for about an hour of driving. The only thing I did not clean was the solenoid entry and exit points. I’m assuming the system is choked again from some leftover gunk. Since the solenoid works with the coolant system I will mention the car used to take a long time to heat up and reach operating temperature before, recently it has started heating up real quick again. This usually happens when the radiator might be choked a little. Last time I fixed this issue by opening the drain and running some water from a hose pipe through the radiator. The fast heating up came first followed by hesitation on acceleration. So at the moment I have 3 things to look at. First, unclog the throttle again. Second, Flush the radiator. Finally open and clean up the purge solenoid. Hopefully after these three things the car will run smooth again without the fluctuations in rpm or hesitation during acceleration.

Clean the throttle body, air idler valve, ports with carb cleaner. Utube how to do it. There are 4 bolts, two plugs, and a few hose disconnects. If this doesnt fix it. Replace throttle position sensor and/or air idler which are connected to the throttle body.