Date: Wed, 30 Jul 2003 09:38:36 GMT From: Paul Halliday <pjghnopsamyonder.co.uk> Subject: Mixture problems and lumpy idle
I hope someone can help me with my mixture problems that are driving me crazy. My '89 900 T8 had been running fine through the colder weather (under 20 degC external temperature), but when the weather changed a couple of months back my car started to suffer overheating problems and racing idle RPM, which was up to about 1500 RPM at times. I took a look and concluded that the throttle dashpot was too close to the throttle butterfly. In certain circumstances, the idle would return to normal (about 850/900 RPM) and with just a slight touch on the accelerator pedal the idle would shoot up to 1500 RPM. Okay, that solved the first problem. I've backed off the dashpot to a point that I'm happy with. From a 3000 RPM tug on the cable, it takes about 5 seconds to return to idle at about 900 RPM. Any further back and the car can stall while warming up. More recently, the idle has been lumpy (not hunting) and I've taken some time yesterday fine-tuning the throttle stop grub screw. The screw was set to the o'clock position, so I backed it down a quarter of a turn. The car would not start without a touch on the accelerator cable, so I presumed it needed more air. I turned the screw in an eight of a turn towards the o'clock position and it seems good now. I've tightened the accelerator cable a little (which was quite slack) and re-adjusted the dashpot to suit. I now have a good warm idle at about 950 RPM and from 3000 RPM it takes about 5 seconds to return to idle. But ... It's still lumpy. Also, from cold, the idle is way too low at about 600 RPM. One more thing. Since yesterday, at top boost I get knock - I presume that can be seen when the needle on my calibrated boost gauge snaps back a couple of PSI at top boost and then returns to top boost. I'm having trouble understanding this one. Am I running too lean? Too rich? What do these symptoms suggest? ... And no, I have not fitted an Ecotek duck fart, vac leak device :) From a cold start, the car is choked - right? Once warm, the car is not choked and the air setting is correct. Right? Do I need to make some adjustment to the mixture screw? If so, which way? I'm referring to the hole between the air filter and the fuel accumulator that takes a 3mm hex plug to adjust. Am I going the right way about this? The Haynes says to set the idle first. Am I doing this right? It then says to set the mixture correctly by measuring the exhaust gas. Is there something I can buy to check this? I have no cat, so I presume I can measure the gas at the rear of the car at the exhaust outlet. Any help would be very much appreciated. TIA, Paul 1989 900 Turbo S http://saab.go.dyndns.org/
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