I changed the timing belt on my Accord and when I start it the engine immediately revs up towards 5K and I shut it down instantly.

This is a 1999 Accord LX sedan 2.3L a/t with a ULEV-VTEC F23A4. The car has 220,000 miles and this is its first timing belt replacement. I recently purchased it from the original owner who claimed the timing belt was never changed. So I bought a kit from Continental with both belts, both tensioners, and the water pump. I also replaced the 3 oil seals, 2 drive belts, and the entire 3-piece timing cover.

Before the swap the car was running fine with no quirks or issues. I drained the coolant before the swap and filled it up afterwards. I purged air out of the system with the bleeder on the thermostat housing and I manually squeezed air bubbles out of the upper & lower radiator hoses. The air intake system is unobstructed and the throttle body appears to be functioning properly. The only vacuum lines that were touched were whatever was removed from the valve cover and they were all re-attached without damage. In removed the battery cable, connected the leads together for about an hour to discharge the system, and reconnected the cables to the battery.

I still get the same condition. I start the motor and it revs right up past 4K rpm and I immediately shut it down before it hits 5K. Does anyone have experience with this issue? Can anyone suggest something I may have overlooked?

I triple checked all the timing marks. When the engine over revs it does not make any unordinary sounds like valves slapping due to the engine out of time.

I did unbolt the crank sensors to clean the area around them. If I inadvertently damaged one or both of them could that cause these high revs?

 

For it to rev that high on it's own either your throttle cable is stuck or you have a massive vacuum leak somewhere.

 

I don't think the throttle cable is stuck because I can see it moving freely at the linkage on the throttle body and I have normal movement at the pedal. The butterfly on the throttle body is closed as it should be when I turn the key ON before I start it. Aside from the timing components I did not disturb anything besides the PVC and other vacuum fitting on the valve cover. Both went back on with no damage.

It's too much of a coincidence (although not impossible given my luck) for another random component to fail while in the middle of another non-related service repair.

Correct me if I'm wrong here but if the timing was off then I would have destroyed the valves by now after repeated attempts to start the motor at 4K+ rpm. And if the timing was off it shouldn't cause the high revs. I don't think the balance shaft would cause the high revs if the timing was off on that - it should only cause it to shake or run rough from vibration.

Where logic and reason fail me is with the crank sensors. I removed them to clean them. The wiring is old. I was careful but if a wire broke and I did not notice it then would a faulty signal from one or both sensors cause a high rev condition?

I have no problem tearing this down again but I would like to have something to look out for during the process. I do not have a service manual. Perhaps if anyone can share what resistances I am supposed to get on the crank sensor harness testing towards the sensors I can trouble shoot before I start the tear down process. Thank you.

 

Easy solution to begin your diagnostics. Unplug the crank sensor and start it and see if it is still revving to the sky.
You can actually check the wiring of the crank sensor if it worries you,.

Re the timing I can't see how it can rev that high from a timing issue alone.

I know it sounds sort of ridiculous but are you sure you connected the PCV valve / vac hosing to the correct place on the intake?

 

Crank sensor is definitely not going to cause the car to rev on it's own. If it's bad the car just won't run or will run extremely poorly and you'll get a CEL.

If the throttle body is working normally, then you have a big vacuum leak somewhere. The only way the engine will continue to rev without the throttle body opening is if air is getting in somewhere else. Since it's revving as high as 5k it should be a fairly large leak. Probably either the brake booster line or the PCV line.

 

I appreciate all the words of advice. I fixed the problem.

I agree that an engine out of time will not rev uncontrollably like this. And I definitely did not mix up the PCV and vacuum hose - they only fit on one way and physically aren't long enough to mix up. I tested some resistance (roughly 2K ohm) on each of the crank sensors. When I unplugged the sensor harness the car wouldn't start. This makes sense. It also means if I had a broken wire (open condition) on one of the sensors then the car would not start. This ruled out the crank sensors.

I took another look at the throttle linkage at the throttle body. There are two cables. The one from the pedal was fine. The other cable was the problem. It goes to a canister on the left fender. I think it has to do with the cruise control. I unplugged the wire harness for this device and the car started and revved normally. There was too much tension on this cable. I let out some slack, plugged the harness back in and the car runs beautifully.

I swear I did not disturb this cable while changing the timing belt. I'll have to chalk it up to gremlins messing around under the hood. I cannot explain how this happened but I'm glad the problem is solved.




On the back of the valve cover is the PCV valve dead center and a vacuum hose on the left corner going to the air intake. You can also see the throttle linkage and cables behind the valve cover.

The bottom cable on the throttle linkage goes directly to the pedal in the cabin. The top cable goes to this canister which may be part of the cruise control? Unplugging this cleared the high rev condition. I let out some slack at the adjuster on the throttle linkage and plugged the harness back in. Problem solved.

 

Glad you got it sorted and thanks for the pics! Can be really helpful to anyone else who may have a similar issue,

 

Hey I just wanted to thank you for your tip. Just did water pump timing belt on 01 pt cruiser and first start did this exact same thing . I was stumped almost had a tear thinking I'd have to retire it. But checked the cables like you said and bam fixed no more high revs and idles fine .. thank you so much...

 

I just created an account solely to come on here and thank you for starting this thread and posting your fix. I too just did a timing belt and a bunch of other things while it was apart only to find it revving high when started. Freaked me out I did something very wrong. Searched google and came across this, ran out to my shop and found this exact problem, something I would have never checked. So thank you for asking and finding this fix. I appreciate it and it definitely took some stress off my shoulders lol.

 

I just wanted to say, your my hero right now. I had same issue just now on a2001 Honda Accord. Replaced water pump and timing belt only to start up and rpms went thru the roof. I was terrified. I found your thread, BAM. problem solved. Thanks.