1987 944 proper startup behavior
01-26-2020, 06:50 PM
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1987 944 proper startup behavior
Hi Guys - Hoping you guys can help me with a problem that may not actually be a problem. My 944 is a stock, well sorted '87 that runs strong and has a ton of new parts. I bought it in 2015 as a non-running project and have now made it good enough that it could be a reliable daily driver. However, I am not happy with the way the idle behaves. This is the only 944 I have ever experienced, so I am not 100% sure what is considered normal.
On a cold start, it starts and idles at about 800 rpms - maybe a little lower. Should it be higher? If I give it gas, it will rev fine and settle in at about 800 again. As it is driven and the engine warms, the idle climbs to about about 1000 rpms - sometimes higher. This is with no real load on the engine. If I turn on the lights, fog lights, fan, etc. the idle drops to about 850 or so. If I turn those things off, it stays at 850. If I turn on the A/C, the idle drops to 800. If I turn it off, it climbs to about 850 and stays there. Drive it around with no accessories again and we're back to 1000+. I've checked for vacuum leaks.
Basically, the idle is all over the place based on accessory usage and engine temperature. That just doesn't seem right. I feel like I am chasing my tail, but I can't imagine it behaved this way in 1987. Any insights would be appreciated. BTW, the DME coolant temperature sensor is new and the DME is freshly refurbed with a stock chip.
I should probably add that after a drive and the car sits for 30 minutes or so, it idles rough on startup. After 30 seconds or so it settles down and idles smoothly. This only happens occasionally.
Thanks,
John
On a cold start, it starts and idles at about 800 rpms - maybe a little lower. Should it be higher? If I give it gas, it will rev fine and settle in at about 800 again. As it is driven and the engine warms, the idle climbs to about about 1000 rpms - sometimes higher. This is with no real load on the engine. If I turn on the lights, fog lights, fan, etc. the idle drops to about 850 or so. If I turn those things off, it stays at 850. If I turn on the A/C, the idle drops to 800. If I turn it off, it climbs to about 850 and stays there. Drive it around with no accessories again and we're back to 1000+. I've checked for vacuum leaks.
Basically, the idle is all over the place based on accessory usage and engine temperature. That just doesn't seem right. I feel like I am chasing my tail, but I can't imagine it behaved this way in 1987. Any insights would be appreciated. BTW, the DME coolant temperature sensor is new and the DME is freshly refurbed with a stock chip.
I should probably add that after a drive and the car sits for 30 minutes or so, it idles rough on startup. After 30 seconds or so it settles down and idles smoothly. This only happens occasionally.
Thanks,
John
Last edited by Joe6pack; 01-26-2020 at 07:16 PM.
02-02-2020, 09:26 AM
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Cruisin'
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The car should hold idle speed better than it's doing. There are a lot of factors that can influence idle quality - vacuum lines are a good start and I would check them again. I would also find every electrical connection to the engine under the hood (temp sensors, MAF, idle control valve, etc, including the grounds) and pull them off, clean them with brake-clean or electrical contact cleaner,and mate them back up.
The next step would be the idle air control valve - you can clean these, but at this point it's probably original and should be replaced. It's under the intake, so that has to come off to access it. Check Clark's Garage if you are unsure how to remove/reinstall.
It's possible the injectors are dirty and contributing to the issue as well - Mr. Injector is who I use to have these items cleaned. Good price, fast service...
The next step would be the idle air control valve - you can clean these, but at this point it's probably original and should be replaced. It's under the intake, so that has to come off to access it. Check Clark's Garage if you are unsure how to remove/reinstall.
It's possible the injectors are dirty and contributing to the issue as well - Mr. Injector is who I use to have these items cleaned. Good price, fast service...