1988 300e surging at idle
 

I have a 1988 300e with 145000 km on the engine. At idle, there is a rhythmic surge in the engine. About every second, the RPMs increase about 50 rpm and the oil gauge fluctuates between 1 and 1.25. Sometimes the car vibrates. I have had the plugs, wires, rotor and cap changed as well as the air flow meter. The head gasket has been changed as have the valve seals.

Is this normal?

The car has intermittent hesitation problems (very little power for about 5 seconds) when starting off, especially when cold ( about 1 in 10 times). It seems to be a bit worse in wetter weather. The hesitation gets better as the car warms up and most of the time disappears. I can get rid of the problem most times by tapping the accelerator a few times. Whenever a floor it, the car responds almost immediately.

There is never a problem starting but sometimes (1 in 10), the RPMs drop to 100 and the car almost but never stalls.

Could this be an OVP problem? (The fuse is working)

I've had my car to the mechanic twice in the last month for this and the car refused to show the symptoms both times- using both hot and cold starts.

Any suggestions?

walpoleb,

I have a similar pattern of behaviour on my recently acquired 5-speed 300E of the same year as yours. It is intermittent though, and is less of an issue when the car is driven more. It does stall when still warming up sometimes, but that is also not a real problem, just put the clutch back in and it restarts immediately. I have no solution to offer, but will be watching for an answer to your post from someone knowledgeable on the subject so I can check my car out too.

Other than letting you know someone else is in the same boat, I guess this post is kind of useless to you. I hope an answer arrives soon though, and Good Luck (to both of us), Jim

Thanks Jim. I guess I forgot to mention my car is an automatic.
I hope someone has some suggestions for us.

i remember having the same problem before whereby
the car seems "breathing" and revving by itself.
the OVR fixed the problem in my case.

do you have the updated OVR with the red top and
two fuses on top? if not, before trashing the old one,
why not replace the old fuse and see if it solves the
problem. good luck!

Good morning. I read a thread a while ago that addresses your problem The post describerd the idle air bleed assembly being gummed up leaving the computer unable to seemlessly regulate the idle. He said he was told to replace it but disassembled it instead, thourghly cleaned it , reinstalled it and solved the problem .If you do a search you may find the same reference point. Good luck.
Brian

Thanks Jim, Joel and Brian.

The fuse is working. I'm not sure which OVP is in there now but it is original. I'm having it changed today. I'll get the idle air bleed checked and keep you posted.

Does anyone know if it is a problem ordering sensors through US companies for delivey in Canada?

Thanks.

Bob

if ever you have to order and import from the U.S., please
patronize Fastlane. no problem in importation, so long you
pay the duties, and taxes.

Hi everyone.

No change in performance. Just changed the OVP, had the idle air bleed, throttle position sensor, temperature sensors, vacuum hoses,ignition coil , rotor & wires checked. All were in good shape.
Don;t know what to do next.

I just had the same type of trouble with my car, it turns out it was the oxygen sensor , there is a couple things that could also cause this the idle control valve which u can check by spraying it with carb cleaner turn the ignition on to see if it clicks or vibrate , you can also check the EHA valve to see if it leaks if it does change it but i am pretty sure it is ur o2 sensor i just replace mine with a ford mustang 302 eng 5.0 cost me $37 at auto zone

Thanks Maximus.

I'll check the o2 sensor out.

The oxygen sensor does not come into play when its cold. Were your spark plugs clean when they were changed or were they oil fouled? You may have some oil leaking down past the valve seals and guides that may give problems when cold or at idle that may seem to disappear at speed. Also check you vacuum lines. Does the vacuum read a little low? Spray around the rubber lines and injector seals with some W/d 40 to see if there is a change in idle speed.

Hi JDUB.

I was getting some coolant in the cylinders 1.5 years ago. Valve seals were changed. Head gasket changed. Plugs were changed and were clean when I last inspected them (about 4 months ago). No leaks apparent in vacuum system, although I haven't had the vacuum level checked. Are injector seals easy to check?

I've heard a leaking EHA could be the problem? How do you check it?
All my problems exist ,hot or cold. This makes you think the o2 sensor is not the culprit?
Thanks.

Bob

Did you check/replace the coolant temperature sensor located at the back of the head?

~Paul

____________________
'91 300E, 211K miles

I had a similar problem on my 88 300e some months ago. I replaced the vacuum line that runs from the air filter down to the fuel regulator (I think) and that solved the problem. My car had got to the point where it was even stalling now and then. The vacuum lines may appear to be fine, but you need to check them with a guage. I'll bet you have a vacuum problem.

surging E-420
 

Same exact problem my '97 E420. Had from when it was new. Back when it was new the dealer tried and tried to fix - and finally could not so what they did was move the idle up somewhat so that it idles faster. That basically corrected in that the surges are less noticable and on the downstroke it no longer hiccups like it wants to stall. Only problem is that with the faster idle I have to press harder on the break to keep the car stopped. Therefore I drive in the "w" mode, rather than "s", which means the car starts in 2nd gear instead of 1st. Actually this is not so bad, as the E420 has so much power, it is fairly jerky starting in first gear, and I sort of like starting in 2nd (same as my old '87 420 sel did). Sorry this doesn't help you - but now you know you can reprogram to boost the idle and it will be much improved if you can live with that.