Author Topic: When my car is cold started it runs rough (Read 2799 times)

falcontron · « **on:** December 09, 2008, 06:02:58 pm »

I Seem to be having a minor cold start problem with my 97 Jetta 1.9 AAZ Turbo Diesel. When my car is cold started it runs rough / Idles 725-750 RPM for the first 6-10 seconds then the idle kicks up to 1000 RPM then to 1200 RPM. After the car warms up it kicks the idle down to approximately 900RPM. I feel everything except the first 7 to 10 seconds is normal. Any Ideas as to what the problem may be? Vacuum unit?

Vincent Waldon · « **Reply #1 on:** December 09, 2008, 07:23:20 pm »

It can take 5-10 seconds for the vacuum pump to generate enough vacuum to pull on the fast idle linkage... but you might want to ensure there are no vacuum leaks that are preventing this from happening quicker.

Are your brakes working well ?

85gti · « **Reply #2 on:** December 10, 2008, 11:25:42 am »

Quote from: "Vincent Waldon"

It can take 5-10 seconds for the vacuum pump to generate enough vacuum to pull on the fast idle linkage... but you might want to ensure there are no vacuum leaks that are preventing this from happening quicker.

Are your brakes working well ?

Mine is having similar issues and blows blue smoke when running rough. My brakes take 2 good pumps to start working properly. If there a prolem in my near future? Thanks

Vincent Waldon · « **Reply #3 on:** December 10, 2008, 11:45:52 am »

Quote from: "85gti"

Quote from: "Vincent Waldon"
It can take 5-10 seconds for the vacuum pump to generate enough vacuum to pull on the fast idle linkage... but you might want to ensure there are no vacuum leaks that are preventing this from happening quicker.

Are your brakes working well ?

Mine is having similar issues and blows blue smoke when running rough. My brakes take 2 good pumps to start working properly. If there a prolem in my near future? Thanks

The OPs diesel is an AAZ engine that has a vacuum-activated cold idle circuit driven off the same vacuum pump that powers the brakes. So, problems with the vacuum pump might show up as a idle issue *and* a "brakes are hard to push" issue. The OP mentions a "my car has a low idle that gets better" problem.

The problems you're reporting are "hard starts with blue smoke when cold" and "I have to pump my brakes to get them to work"... likely a different set of unrelated issues.

Your engines (assuming you're talking about the ones listed in your sig) are an earlier generation that uses cable-driven cold idle... driven off the cold start handle. So the two are not likely related.

Cold start problems can be compression, glow plug circuits, wrong oil, low battery, poor starter, among others.

Needing to pump the brakes can be master cylinder issues, air in brakelines, problems with a slave cylinder, rear brake proportioner, among others.

falcontron · « **Reply #4 on:** December 11, 2008, 07:09:11 pm »

Vincent Waldon Posted: Tue Dec 09, 2008 11:23 pm Post subject:

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It can take 5-10 seconds for the vacuum pump to generate enough vacuum to pull on the fast idle linkage... but you might want to ensure there are no vacuum leaks that are preventing this from happening quicker.

Are your brakes working well ?

Thanks for responding Vincent. My brakes seem to be ok. When you say vacume pump do you mean vacume brake booster? or is there another vacume pump on the car?

Vincent Waldon · « **Reply #5 on:** December 11, 2008, 07:42:58 pm »

Good to hear *your* brakes are fine !!

The vacuum pump that drives the brakes also drives the fast-idle circuit via a tee off the big plastic line that goes from the vacuum pump to the brake booster bolted to the firewall.

falcontron · « **Reply #6 on:** December 11, 2008, 08:00:09 pm »

Vincent

If you turn the car off when its warm should the vacuum pump hold the pressure for a couple of hours or overnight? It it possible that the plastic hose is ruptured? or the in line valve is passing? If I pump the brakes when the car is cold ( before cranking ) will this build pressure in the vacuum pump that will in turn pull on the fast idle linkage?

Smokey Eddy · « **Reply #7 on:** December 11, 2008, 09:59:03 pm »

The vacuum pump goes where the distributor goes on the gas engine. Take the hose off, start the car and it should suck fairly hard.

always a good check to make sure the pump is working.

Brakes are very important! as we all know.

jtanguay · « **Reply #8 on:** December 12, 2008, 05:25:24 am »

sounds to me like it could be a few issues here... timing slightly off (if you're getting any smoke), a bad glow plug, air in the lines... but hopefully its just the idle speed boost vacuum issue like Vince said.

falcontron · « **Reply #9 on:** December 12, 2008, 05:18:12 pm »

Quote from: "jtanguay"

sounds to me like it could be a few issues here... timing slightly off (if you're getting any smoke), a bad glow plug, air in the lines... but hopefully its just the idle speed boost vacuum issue like Vince said.

Does any onr know how to check if there is air in the lines?