Car idles rough and runs rough at certain rpm


#1

Have a 2001 Civic DX, Manual Transmission, 228K miles. 1.7L SOHC.

Recently changed front motor mount and timing belt on the same day.

I noticed the car running rough and is only rough at certain RPM. Here are the rpm ranges it runs rough, 700rpm which is idle, 2200-2400rpm and 3400rpm approximately. It idles at 700rpm which I believe is the idle rpm on my car, so thinking my timing is not off. One more thing I noticed is if I have AC on and reving down in rpm it sounds like it is about to shutoff (never shuts off) and get a stronger vibration and same thing when I turn the AC on at idle. With ac on my rpm are 720rpm give and take a few. I been driving with above symptom for 300mi+ so far, even got it upto 95mph, don’t know if it is an indication of anything. Got new spark plugs installed at 220K miles.

Could it be the motor mount or my harmonic balancer is out of balance. I did have to use 3/4" impact wrench to knock the harmonic balancer bolt loose. It is a little rusty given I got 228K miles on it.

I am just dreading the thought of my timing being off by a tooth, me and my friend checked the timing marks per oem manual, he checked the cam shaft pulley marks and I did the crankshaft. When we installed the timing belt I only turned the engine counter clockwise so I would not cause a problem with timing belt slack. My AC belt may be a little too tight as well.

The motor mount I put in was an aftermarket one that I bought from amazon. But I have put in aftermarket mount before on the same car and never had anything like this. I am planning to loosen the motor mount, shake the engine, tighten them back up and see if it makes a difference. May be the engine is not seated properly.

Any help will be greatly appreciated.

Sorry for writing a novel but wanted to give the whole story.

Thank you.
Ashok Anumula


#2

Pull the idle air control valve (IAC) off and clean it. With that mileage it likely needs cleaning. That may solve the idle roughness and low idle with AC on.


#3

Where the timing marks for crank/cam still lined up when you applied the tensioner to the timing belt?

Tester


#4

Tester, I believe they were. Will the idle rpm be off if timing is off? I am not sure. Only thing I can do is to take the valve cover off rotate the harmonic balance to tdc and see if the timing marks on cam shaft line up with the head. Thinking TDC mark on harmonic balance should be good enough to show if I am a tooth off.

I may do the IAC as well. Never removed it on this car so got to go see if it is easily accessible.


#5

It’s not the IAC valve.

If you’re at 2200-2400/3400 RPM’s, the engine is off idle. So the IAC valve isn’t the problem.

Tester


#6

I have a friend with a 1993 Accord with the same problem, but only at 2500-2800 rpm area. Idles great, tho. We’ve only tested the TPS so far and it tested fine. We’re planning on testing the mag pick-up in the distributor next. Does the 2001 have a distributor?


#7

@‌ BustedKnuckles. The 2001 does not have a distributor. It has has a hall sensor. No timing adjustment what so ever through mechanical adjustment, not sure electronically via ecu.

Did front motor mount front & timing belt so it has to be one of those two causing problems. Cause engine was not rough before the repair. I did loosen the side mount on the engine (driver side) to see if I can seat it properly, will try to loosen the front one as well and see what happens.

Anybody who did timing belts before, do you think it is possible to adjust one tooth by just taking the top cover off. Get harmonic balancer to TDC by aligning with marks on cover & then slide the belt of the top camshaft, get the camshaft to position and slide it back on.

Ashok.


#8

"Anybody who did timing belts before, do you think it is possible to adjust one tooth by just taking the top cover off. Get harmonic balancer to TDC by aligning with marks on cover & then slide the belt of the top camshaft, get the camshaft to position and slide it back on. "

I’d be very surprised you could get enough slack in the timing belt to do this. First things first, check the cam timing.


#9

One of the mistakes people make when installing a timing belt is, not all the slack of the timing belt is on the tensioner side of the timing belt.

If there’s any slack in the timing belt on the opposite side of the tensioner and the tension is applied to the belt, that slack will cause the cam sprocket to rotate slightly causing the valve timing to be off.

Tester


#10

Alright took my timing cover cover of yesterday. Rotated the engine CCW 4 revolutions, and all the timing marks align properly. I had no tools to take the harmonic balancer off since I could not lock the engine in place, so I checked against the timing marks on harmonic balancer to the cover, and they are dead on. [ Harmonic balancer is keyed to the crankshaft ]

So next culprit may be harmonic balancer is out of balance, it is a little rusty so when I took an impact wrench to get the bolt out rust flakes may have thrown it out of balance! This theory is way up there, as the car talk brothers would say.

Next from motor mount which is brand new and cheap, could be so damn hard that it is not dampening enough! This theory is up there too…

It idles perfect 700rpm +/20, it if I am lagging or leading on time I would think the idle rpm would be off. May be I got to call the car talk guys

Ashok.


#11

I take it all plugs are in good shape? Does it still idle rough or does it only stumble at the above mentioned higher rpms? It could be a faulty coil or a fuel pressure problem. Have you run a bottle of Techron through it?


#12

Plugs have 10K miles on them. It is only rough at certain rpms as mentioned above.

I think coils are ok cause I do not see loss of power or jerking under load. Do not know about fuel pressure! Not a big fan of fuel system cleaners, afraid of ruining seals…

The roughness I started noticing only after front mount change & timing belt. It could have been there before but broken front mount could have muffled it, theory!!.


#13

“Not a big fan of fuel system cleaners, afraid of ruining seals…”

Techron is the best. I’ve seen it fix problems like yours (never seen a problem). Give it a try.


#14

I use Techron at each oil change. So far no dirty injectors or fuel related problems. All gas contains additives and Techron is Chevron’s additves in a bottle, not diluted.