unstable idle

Hi,

I have an Audi A4 1.8 (1996) non turbo car with cable operated throttle. My problem with the car is the idle is unstable and the fuel consumption is high especially on short journeys.
The symptoms are as follows. When the engine is revved and the throttle released the drvs go down to around 600rpm the gain up to around 1100 rpm and eventually settle to around 850rpm after a few seconds. I read that it may be caused by the throttle pot needing to be adapted. I tried to do this by removing the battery negative lead and turning on the lights to drain any residual power. I then re-connected the battery switched on the ignition and did nothing for 30 seconds. I then switched off the ignition and started the car. As a result of doing this the problem had got much worse and the revs fluctuated between 300 revs and 1200 revs and took even longer to settle. After a few days driving the problem went back to the way it was before doing the adaption. I now think that the problem may be related to the Maf and to test this I removed the Maf cable at idle and the car did not change at all.

How can I determine if it is definitely the Maf that is causing the problem or some other cause. I have just got the Ross Tech VAG-COM interface and am learning how to use it so will be able to take a few readings from the ECU.

Regards
Tom

Well, if its a 1.8, then it is a turbo.

See if you are getting any error codes and post them.

It was probably worse for the short time until the ecu reset compltely, usually about 40 miles.

Does it idle about 900 after it runs for a few? If so, its probably related to the idle control that adjusts while the car is warming up. It probably wont cause you too much grief.

If it runs fine after the warm up period, then its probably not the MAF, because it would run ****tty all the time if the MAF was bad.

Look for codes, check the engine bay for loose vac lines, and seach the forum for "rough idle".

Audi has 1.8, 1.6 versions non turbo engines outside of the US. Maybe he is in another country

OMG, I can't even imagine a 1.6 or 1.8 without the turbo! Thats almost like dangerous! make sure no ones coming when you pull out on the road!

Arif, when do you move?

I'm moving this friday.

quote:

ORIGINAL: acetrebo

OMG, I can't even imagine a 1.6 or 1.8 without the turbo! Thats almost like dangerous! make sure no ones coming when you pull out on the road!

That's because they pay about $9 a gallon

It is a 1.8 non turbo(european version). The power is not all that bad as it runs high compression using at least 95 octane fuel. The power is about 125bhp with instant throttle response which makes up somewhat for the lack of a turbo. It is Would still prefer a turbo though.

I cannot do any scans today but will get some tomorrow. What parameters should I be logging? What is the normal effect of removing the Maf cable while the engine is idling?

Regards
Tom

im in the uk had the same 1.8 20v a4 before and had exacly the same problems.

MAF and throttle body may nee replacing , also try to set the throttle body basic setting.
try cleaning the throttle body and inatke,
and disconnect the battery and connect again and tou will see the pointer setting itself, this should temporarily resolve the problem.

I have the very same problem on my A4 but interestingly if the rear of the car is lower than the front (ie on a hill) there is no problem but if it is the reverse I struggle to even start the car. My helpful colleagues here suggest I get some real big front tyres to keep it permanently leaning back.

Or keep a lot of heavy tools in the back. Not much help to me though!!

how about Idle Control Valve ?

check this out

http://www.audiforums.com/m_311488/tm.htm

HI,

I did some logging with the VAG-Com during the weekend. I did the full thottle test of the MAF to check its operation. The following is the log file for blocks 1, 2 and 3. I had cleaned the MAF before doing the test.

Monday,30,October,2006,16:15:27
8D0 907 557 C,,1.8L R4/5V MOTR HS D08,

,Group A:,'001,,,,Group B:,'002,,,,Group C:,'003
,,Engine RPM,Engine load,Throttle angle,Ignition timing,,Engine RPM,Engine load,Inj. period,Mass air flow,,Engine RPM,Battery voltage,Coolant temp -G62,Intake air temp
,TIME, 820..900, 0.85..2.50, 0..5,12deg BDTC,TIME, 820..900, 0.85..2.50 , 2.0..5.0, 2.0..4.0,TIME, 820..900,10.0..14.5, 80..105,19.5=>see lbl file
Marker,STAMP, /min, ms,°, °ATDC,STAMP, /min, ms, ms, g/s,STAMP, /min, V,°C,°C
,140.91,1640,3.30,20.8,26.3,141.22,2000,1.75,2.32,2.29,141.57,1680,13.940,64.5,19.5
,141.89,1320,1.05,6.9,18.0,142.22,1080,1.45,2.49,4.65,142.58,800,13.940,64.5,19.5
,142.98,880,2.70,4.8,12.8,143.34,920,1.75,3.44,2.57,143.64,760,13.940,64.5,19.5
,143.99,640,2.00,9.1,20.3,144.30,680,2.55,4.82,4.31,144.68,800,14.008,64.5,19.5
,145.02,800,1.85,5.2,17.3,145.39,720,1.80,3.61,3.26,145.73,560,13.872,64.5,19.5
,146.12,800,2.85,3.5,18.8,146.45,880,1.90,3.44,3.06,146.85,720,13.940,64.5,19.5
,147.19,720,2.20,7.4,21.8,147.54,760,2.15,3.44,3.40,147.89,760,13.940,64.5,19.5
,148.27,680,2.20,9.1,20.3,148.62,760,2.30,3.61,3.61,149.01,800,13.940,64.5,19.5
,149.39,760,2.15,7.8,23.3,149.76,760,2.20,3.44,3.96,150.10,760,13.940,64.5,19.5
,150.39,800,2.20,8.2,22.5,150.71,840,2.15,3.53,3.89,151.06,840,13.940,64.5,19.5
,151.37,840,2.15,8.2,15.0,151.67,800,2.20,3.61,4.09,152.03,840,14.008,64.5,19.5
,152.34,840,2.20,8.7,13.5,152.65,840,2.15,3.70,4.09,152.95,800,13.940,64.5,19.5
50,476.65,840,2.25,8.7,12.8,476.99,840,2.25,3.78,4.31,477.31,840,13.668,70.5,19.5
,477.65,840,2.30,8.7,14.3,478.03,840,2.30,3.70,4.31,478.40,840,13.736,70.5,19.5
,478.75,840,2.30,8.7,12.8,479.07,840,2.25,3.78,4.31,479.46,840,13.804,70.5,19.5
,479.79,840,2.30,8.7,12.8,480.13,840,2.25,3.61,4.23,480.44,840,13.804,70.5,19.5
,480.81,840,2.30,8.7,12.8,481.13,840,2.35,5.93,6.87,481.48,1040,13.804,70.5,19.5
,481.88,1600,2.45,8.2,27.0,482.23,1280,1.45,2.67,3.82,482.55,960,13.736,70.5,19.5
,482.94,880,2.10,8.2,18.0,483.29,840,2.10,3.27,4.03,483.59,680,13.736,70.5,19.5
,484.00,560,2.85,11.7,12.8,484.37,680,3.40,6.02,4.86,484.76,920,13.736,70.5,19.5
,485.14,1080,2.45,9.5,20.3,485.49,1080,1.85,2.67,3.47,485.85,880,13.736,70.5,19.5
,486.14,640,2.00,10.0,21.0,486.45,480,3.55,8.00,8.12,486.78,640,13.260,70.5,19.5
,487.08,840,3.40,10.0,3.8,487.43,1080,2.65,3.96,4.37,487.75,1040,13.804,70.5,19.5
,488.07,920,2.00,8.2,20.3,488.39,800,2.30,4.47,5.97,488.68,880,13.736,70.5,19.5
,489.02,1440,3.70,18.7,21.0,489.36,1800,2.85,4.64,9.79,489.73,1880,13.736,70.5,19.5
,490.06,1800,2.90,23.0,30.8,490.42,1800,3.55,7.31,16.39,490.76,1920,13.736,70.5,19.5
,491.10,1840,5.60,35.6,19.5,491.45,1640,6.05,11.35,22.36,491.82,1800,13.736,70.5,19.5
,492.15,2200,6.55,48.6,21.8,492.53,2560,6.80,12.30,38.75,492.87,2800,13.736,70.5,19.5
,493.26,2520,0.80,5.6,15.0,493.60,1720,6.65,14.88,30.34,493.91,2040,13.736,70.5,19.5
,494.29,2240,7.05,82.9,23.3,494.62,2400,7.20,13.76,39.51,494.97,2600,13.804,70.5,19.5
,495.34,2800,7.45,83.3,23.3,495.70,3040,7.60,14.79,50.34,496.06,3240,13.736,70.5,19.5
,496.46,3480,8.00,83.3,24.8,496.83,3720,8.20,16.25,69.09,497.21,4000,13.736,70.5,19.5
,497.60,4240,9.10,83.3,18.8,497.99,4520,9.00,17.20,89.65,498.33,4760,13.668,70.5,19.5
,498.70,5000,8.45,83.3,24.0,499.03,5200,8.35,16.25,93.47,499.39,5440,13.668,70.5,19.5
,499.74,5640,8.50,83.3,29.3,500.09,5880,8.45,16.60,104.23,500.45,6040,13.668,70.5,19.5
,500.79,6200,8.05,83.3,30.0,501.16,5840,0.80,0.95,9.09,501.50,5160,13.804,70.5,19.5
,501.87,4120,3.20,44.3,24.0,502.30,4320,8.60,15.65,81.59,502.68,4440,13.736,70.5,19.5
,503.09,4560,8.65,65.1,18.8,503.47,4360,1.05,0.95,6.53,503.84,3800,13.736,70.5,19.5
51,504.22,3240,0.85,11.7,33.8,504.55,3200,1.05,1.81,7.92,504.92,3200,13.804,70.5,19.5
,505.29,3160,1.45,17.8,39.8,505.63,3160,1.50,2.49,10.48,506.01,3160,13.804,70.5,19.5
,506.36,3120,1.55,18.7,39.8,506.75,3120,1.55,2.58,9.72,507.10,3080,13.804,70.5,19.5
,507.48,3040,1.10,13.5,39.8,507.83,3080,1.80,3.44,14.51,508.17,3040,13.804,70.5,19.5
,508.53,2760,0.75,6.1,23.3,508.88,2360,0.75,1.98,6.18,509.24,2440,13.804,72.0,19.5
,509.64,2440,2.10,20.4,36.8,509.96,2400,2.20,3.70,11.59,510.30,2400,13.804,72.0,19.5
,510.65,2400,2.70,25.6,36.0,511.00,2400,3.00,5.25,16.11,511.32,2400,13.872,72.0,19.5
,511.64,2400,3.75,29.9,33.8,511.98,2400,4.05,7.31,22.15,512.32,2400,13.804,72.0,19.5
,512.65,2440,4.35,31.7,32.3,513.03,2440,4.40,7.65,23.68,513.38,2440,13.804,72.0,19.5
,513.71,2440,4.45,32.1,32.3,514.05,2440,4.00,6.36,18.06,514.40,2440,13.804,72.0,19.5
,514.78,2440,2.40,21.3,36.8,515.15,2440,2.30,3.78,12.01,515.48,2440,13.872,72.0,19.5
,515.84,2440,2.15,19.5,36.8,516.15,2440,2.10,3.53,11.04,516.49,2400,13.872,72.0,19.5
,516.84,2400,2.00,18.7,36.8,517.19,2400,2.00,3.44,10.42,517.55,2400,13.872,72.0,19.5
,517.91,2400,1.90,17.4,36.8,518.29,2360,1.90,3.27,9.86,518.62,2360,13.804,72.0,19.5
,518.98,2360,1.85,16.9,36.8,519.31,2360,1.85,3.10,9.72,519.70,2360,13.804,72.0,19.5
,520.05,2360,2.35,21.7,36.8,520.44,2360,2.60,4.56,13.89,520.76,2360,13.804,72.0,19.5

I dont know how to attach a file so I included some of the log file. If anyone can tell me how to attach a file I will do it.

Fom what I can see the mass air flow at idle is a little high 4.23 t0 4.31. The maximum air flow is 104.23 which seems ok for a 125 bhp engine.

Also the throttle angle is going from 8.7 degrees min to 83.3 degrees maximum (8.7 is a bit big for idle and 83.3 is a bit small for full throttle.

There were some when I started looking last week but after clearing them nothing has come back.

Any ideas what might still be causing the idle problems or what I should try next?

Regards
Tom

Any ideas on this one? I have more logs if anyone wants to see them.

Regards
Tom

Cheers guys for the suggestions. I eventually got around to cleaning the throttle body and doing a throttle body adaption afterwards and not the idle is totally stable. It quickly returns to around 1000 revs above idle and slowly returns to idle speed. It is also much smoother.

Regards
Tom

quote:

ORIGINAL: kajwhite

I have the very same problem on my A4 but interestingly if the rear of the car is lower than the front (ie on a hill) there is no problem but if it is the reverse I struggle to even start the car. My helpful colleagues here suggest I get some real big front tyres to keep it permanently leaning back.

Did you ever figure out what was wrong as my car idles funny and cuts out when the rear is higher than the front, just like what you say. It's very weird.