Date: 31 Jul 2003 00:20:50 -0700 From: alancemornopsamo.com (Lance Morgan) Subject: Re: Mixture problems and lumpy idle
Paul Halliday <pjghnopsamyonder.co.uk> wrote in message news:<BB4D50AA.7F8F%pjghnopsamyonder.co.uk>... > 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/ Is this K-Jetronic fuel management (discontinued in the USA in 88, IIRC)? Do you have an O2 sensor (which can provide w/warm idle mixture info)? And the overheating hasn't reoccurred since bleeding the system? Lance
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