I have a <u>intermittent</u> idle problem in that it just rough enough to feel a slight shudder in the cabin when the car is warm. The rev needle doesn't move, but you can also see the engine shiver and hear the exhaust note change.
One mechanic suspected my O2 sensor. Interestingly, if I disconnected it, the problem went away. I therefore bought a new o2 sensor and the problem disappear for a few days. However, this morning it came back.
I've a new air filter, have tried various plugs, have tried injection cleaner and have cleaned the throttle body and idle control valve.
My brain is aching from thinking about this. I have been trying to solve this for six months now. Any ideas what would affect idle in such a way? Air temp? Idle stepper motor?
1.8 16v idle problem
Moderator: RichardW
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">One mechanic suspected my O2 sensor. Interestingly, if I disconnected it, the problem went away. I therefore bought a new o2 sensor and the problem disappear for a few days. However, this morning it came back.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
A clue here ?
Could it be the Lambda sensor cabling at fault ? - have the cabling and all connectors been checked thoroughly ?
How about the CTS ?
It's located near or on the thermostat housing - on cylinder head over the flywheel. 2 pole green.
If this is disconnected the engine runs constantly with choke. Try pull the plug and short out the plug. This signals the ECU the engine is hot. You will clearly notice a change in engine idle running if this is the problem.
A clue here ?
Could it be the Lambda sensor cabling at fault ? - have the cabling and all connectors been checked thoroughly ?
How about the CTS ?
It's located near or on the thermostat housing - on cylinder head over the flywheel. 2 pole green.
If this is disconnected the engine runs constantly with choke. Try pull the plug and short out the plug. This signals the ECU the engine is hot. You will clearly notice a change in engine idle running if this is the problem.
Most common causes of idle problems are intake air leaks. Check ALL rubber hoses round the air intake and the rubber boot from the air flow meter for splits. After that it could be the idle control valve (aka stepper motor) being gummed up with oil from the crank case blow by gases. Periodically these need cleaning out with WD40. Next it could be the O2 sensor but you've already changed that. Your ECU may have logged some fault codes so get it on for a diagnostic and get them read. It could save you a load of aggro.
Coolant temp sensor would cause poor cold starting and a misfire, but only when cold. When hot the lambda sensor would kick in (going into closed loop mode) and control the mixture anyway.
Judging by your symptoms I'd say vacuum leak for definite.
Coolant temp sensor would cause poor cold starting and a misfire, but only when cold. When hot the lambda sensor would kick in (going into closed loop mode) and control the mixture anyway.
Judging by your symptoms I'd say vacuum leak for definite.
Thanks for the two thoughtful replys:-
Anders, it's not a cabling fault, as the engine management light comes on if I disconnect the O2 sensor. The CTS sensor was under suspicion when I had strange temp gauge readings on the dash. It ended up being a sticky thermostat. I understand there are two CTS sensors; one for the ECU and one for the temp gauge. I shall try and stick a meter on the ECU one and see how stable the readings are.
AndersDK, all hoses have been checked, cleaned and the ISM is clean. Citroen have looked at fault codes and none ever show up. This suggests that to me that the car is still operating within tolerance, but something is making it go from one extreme to the other - make sense?
Anders, it's not a cabling fault, as the engine management light comes on if I disconnect the O2 sensor. The CTS sensor was under suspicion when I had strange temp gauge readings on the dash. It ended up being a sticky thermostat. I understand there are two CTS sensors; one for the ECU and one for the temp gauge. I shall try and stick a meter on the ECU one and see how stable the readings are.
AndersDK, all hoses have been checked, cleaned and the ISM is clean. Citroen have looked at fault codes and none ever show up. This suggests that to me that the car is still operating within tolerance, but something is making it go from one extreme to the other - make sense?
I wonder whether there is a problem? My Xantia 1.8i 16v idles fine (in that the rev counter is steady) but the engine does slightly shiver. When you stand at the back of the car you can hear the exhaust spit rapidly ever few seconds. I often wondered whether this was problem as I never experienced this on my diesel Xantia. But it has always done it (I have had the car since 40K miles) and it drives normally.
However, do let us know whether you solve it
However, do let us know whether you solve it
Snap !
My Xantia (2000 1.8i 16v) does exactly the same thing at idle. I've had the car from 6 months old and as far as I can remember it's always been a little lumpy at hot tickover. Almost like a misfire on one cylinder now and again but not quite as bad.
Another thing I've noticed is the engine definitely dosn't like engine over-run / braking at idle revs, ie slow moving traffic going downhill in 2nd / 3rd. The car can't seem to make up it's mind what the throttle should be doing.
I've just put both down to the engine management system being a bit flakey at low revs.
Tom.
My Xantia (2000 1.8i 16v) does exactly the same thing at idle. I've had the car from 6 months old and as far as I can remember it's always been a little lumpy at hot tickover. Almost like a misfire on one cylinder now and again but not quite as bad.
Another thing I've noticed is the engine definitely dosn't like engine over-run / braking at idle revs, ie slow moving traffic going downhill in 2nd / 3rd. The car can't seem to make up it's mind what the throttle should be doing.
I've just put both down to the engine management system being a bit flakey at low revs.
Tom.
Sounds similiar to sticking valve(s). When you rev the engine does the shimmer stop or fade away? Next time you change the oil and filter try flushing oil in the system for 15 mins (with a clean filter) then change the filter for a fresh one (seems a waste but you must) and refill with oil and a additive to cure sticking valves. Hope this helps
Snap here too !
My 1998 Xantia 1.8i also spits and runs slightly lumpy at warm idle too, its fine whilst it warming up for the first few minutes, but after that it starts the cough and you can feel it when your sat in the car, and if you listen to the exhaust its like it misses a beat every now and then with a little pop
My 1998 Xantia 1.8i also spits and runs slightly lumpy at warm idle too, its fine whilst it warming up for the first few minutes, but after that it starts the cough and you can feel it when your sat in the car, and if you listen to the exhaust its like it misses a beat every now and then with a little pop
<font color="blue"><font size="2"><font face="Comic Sans MS">Hi,
I have had bucketloads of those problems with my 16v 1998cc Xantia.
In my case it was the inlet manifold gasket blown in two places.
I changed that (without taking manifold off car ), and and all was perfect for a month or so
Car started again doing what yours is, so I nipped inlet manifold bolts up a bit and is running ok again.
Hope this helps you,
Greg</font id="Comic Sans MS"></font id="size2"></font id="blue">
I have had bucketloads of those problems with my 16v 1998cc Xantia.
In my case it was the inlet manifold gasket blown in two places.
I changed that (without taking manifold off car ), and and all was perfect for a month or so
Car started again doing what yours is, so I nipped inlet manifold bolts up a bit and is running ok again.
Hope this helps you,
Greg</font id="Comic Sans MS"></font id="size2"></font id="blue">
Thanks for the all the responses. It's somewhat a relief to hear others experiencing this as well.
The fact that it disappears when I disconnect the O2 sensor suggests to me that it's a lean/rich problem. I assume that when I disconnect the O2 sensor, it goes into open loop and the fine tuning stops. As I have just replaced my O2 sensor, it suggests that there may be another sensor that's causing the air/fuel ratio to change excessively. The only one I'm aware of at this stage is the CTS.
So here is my plan of attack:
1) Check the readings from the CTS. I want to try and see if the readings are erratic when it occurs.
2) Throw some valve cleaner/flush additive in.
The fact that it disappears when I disconnect the O2 sensor suggests to me that it's a lean/rich problem. I assume that when I disconnect the O2 sensor, it goes into open loop and the fine tuning stops. As I have just replaced my O2 sensor, it suggests that there may be another sensor that's causing the air/fuel ratio to change excessively. The only one I'm aware of at this stage is the CTS.
So here is my plan of attack:
1) Check the readings from the CTS. I want to try and see if the readings are erratic when it occurs.
2) Throw some valve cleaner/flush additive in.
Just checked the output voltage on the ECU CTS sensor. With a cold engine and off, it was 2.7 volts. It slowly worked its way down to .36 volts when the fan kicked in. The fan brought the voltage up tp .45 volts.
The voltage changed did seem smooth and it wasn't jumping around. Does this sound like a correctly working ECU CTS sensor?
The voltage changed did seem smooth and it wasn't jumping around. Does this sound like a correctly working ECU CTS sensor?