Technical issue for any mechanics/those in the know

Jono8

Jono8

Jono8

Caporegime
Joined
20 May 2007
Posts
41,034
Location
Surrey
I have noticed that my 2007 Civic 1.8 petrol is not returning to idle very smoothly.

If i rev it, revs will drop as normal till about 1000-1500 rpm where they will then slightly rise again (in spite of my foot being fully off the throttle), and then they will return to the normal 700rpm.

This happens pretty consistently, and i think may be the reason why i have thought it has been a little jerky when coming off the throttle at low speed.

So essentially, i can be sitting at idle, rev the engine, foot of throttle, rpms drop as expected until 1000-1500rpm where the drop will then slow, and there will be a small little increase/rev (done by the car , not me), and then they will go down to proper idle rpms.

When back down, the idle is smooth and at the correct rpms with no issues.

Also, it happens in gear, out of gear, in neutral, clutch in or out etc so its definitely engine related.

There are no warning lights/engine lights and the car otherwise runs fine.

Any thoughts?

My first thoughts are either somehitng is sticking throttle wise, or there maybe a small hose/air leak somewhere. However if there was an air leak, would it really idle so well once it is there?
 
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Like above, MAF sensor probably needs a clean as does the IACV (Idle Air Control Valve). Quite common on the Honda petrol engines of most ages to be honest, nothing to fret over :)
 
Thanks. Will give the MAF sensor a clean first of all as that looks like a very easy DIY job.
 
Cleaning/replacing the MAF is the likely solution. Use a proper MAF cleaner as the hotwire elements are sensitive to damage.

Sticking throttle would likely give you DTCs relating to throttle performance

bJN said:
Like above, MAF sensor probably needs a clean as does the IACV (Idle Air Control Valve). Quite common on the Honda petrol engines of most ages to be honest, nothing to fret over :)
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2007 will be drive-by-wire era so no IACV
 
Frozennova said:
Cleaning/replacing the MAF is the likely solution. Use a proper MAF cleaner as the hotwire elements are sensitive to damage.
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yeh, have read about this. Have ordered some proper MAF cleaner which is arriving tomorrow.

Strange that it is just that rev range between 1000-1500rpm that causes the issue.
 
When the maf sensor packed in on my pulsar I would get hunting idle, generally rough running and it caused the car to run on a safety map which would enrich the fuel mixture to prevent possible detonation. Might be worth changing the oil as well.
 
Jono8 said:
yeh, have read about this. Have ordered some proper MAF cleaner which is arriving tomorrow.

Strange that it is just that rev range between 1000-1500rpm that causes the issue.
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The sensing portion of the MAF is a heated wire, the current required to maintain a set temperature is used to measure the airflow.

When they become "dirty" the amount of current required changes due to the insulating effect, as the airflow increases the insulating has has less of an impact
 
My friends old (EP) 1.6 civic has an issue similar to this, revs would hang and sometimes idle would be particularly lumpy. We stripped and cleaned the VTEC solenoid which cured it for a time, came back every couple of years but again stripped and cleaned to resolve. I'm not overly familiar with the 1.8 but assume it has a similar setup

I'm near certain his car was throwing a code with it though, assume you've checked yours (I know there's no warning light on at the moment )?
 
rodenal said:
My friends old (EP) 1.6 civic has an issue similar to this, revs would hang and sometimes idle would be particularly lumpy. We stripped and cleaned the VTEC solenoid which cured it for a time, came back every couple of years but again stripped and cleaned to resolve. I'm not overly familiar with the 1.8 but assume it has a similar setup

I'm near certain his car was throwing a code with it though, assume you've checked yours (I know there's no warning light on at the moment )?
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Haven't checked anything with a code reader, but had no warning lights at any time with the car.
 
For anyone interested, I tried cleaning the MAF and it made no difference. Air filter looked a bit grubby too so changed that - no difference.

After doing some research it seemed like people who had cleaned the throttle body and not reset the throttle position sensor via a computer had this exact issue. The TPS in these does not reset with the battery being disconnected and has to be done electronically.

Now i had not cleaned the throttle body, but figured that maybe it was in need of a clean and then a reset (to reset the TPS, you have to clean it first anyway). So, I cleaned the throttle body myself and as expected this made the issue even worse (before the reset). Took it to my local guy who reset it for me via the proper computerised method for £40 and now it is back to normal.

It still stops/blips like 50-100rpm when it reached 1000rpm but i believe this is normal and most cars do this when revs are coming back down. Before it would surge back up to about 1500rpm. It also doesnt hold at 1500-2000 rpm when putting the clutch in whilst going along. It will instantly go to idle speed as it should.Car is much less jerky at low speeds now and doesnt have a rev hissy fit between 1000-2000rpm.

Not sure why it would suddenly start doing it though? Is it because it hasnt been used much for most of the year? Would that somehow make the throttle body dirtier potentially (ie no airflow through it for ages). Maybe the carbon/much just sat there and caked itself on :p
 
bainbridge said:
It's a 14 year old car and you got it running much better for £40, that's a win in my book. Maybe a long drive might help it settle down?
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Indeed! It is always quite gratifying to have diagnosed and fixed something yourself. It should be getting a few long runs again soon, which will hopefully do it good.
 
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