engine dying when decelerating
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From: Texas
engine dying when decelerating
Took the '89 to Austin over the weekend (Sorry I missed you Ryan. We had a heck of a party without you!) Oil leak was stopped with the addition of a missing grommet around the lower front cam cover bolt.
The car starts and runs great. New LH, R & R the intake, all new fuel and vacuum lines, new idle stabilizer valve, new plug wires, new plugs, rebuilt 4 nozzle fuel injectors. It did start doing something interesting while on the trip. The car runs beautifully at speed, however if I decelerate from any speed (highway or city speeds) and the idle gets less than 2K RPM, it will begin to sputter and run rough and the engine will usually die. I found that if I keep the RPM's above 2K, it runs fine and stays running fine. About the only thing I did not replace while into my Intake R & R was the throttle switch.
I did replace the fuel pump relay thinking "Relay relay relay" but it didn't make any difference.
Any thoughts or suggestions on this?
The car starts and runs great. New LH, R & R the intake, all new fuel and vacuum lines, new idle stabilizer valve, new plug wires, new plugs, rebuilt 4 nozzle fuel injectors. It did start doing something interesting while on the trip. The car runs beautifully at speed, however if I decelerate from any speed (highway or city speeds) and the idle gets less than 2K RPM, it will begin to sputter and run rough and the engine will usually die. I found that if I keep the RPM's above 2K, it runs fine and stays running fine. About the only thing I did not replace while into my Intake R & R was the throttle switch.
I did replace the fuel pump relay thinking "Relay relay relay" but it didn't make any difference.
Any thoughts or suggestions on this?
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From: Long Island and Lake George, NY
Throttle switch.
Quick check, pop the hood and grab the throttle linkage. As you move it off the idle stop, there should be a distinct click. If there is no click, it is not returning to idle and trying to fuel it for cruise conditions. I had some similar symptoms and wound up replacing my switch, problem solved, but PIA to R&R.
Jim
Quick check, pop the hood and grab the throttle linkage. As you move it off the idle stop, there should be a distinct click. If there is no click, it is not returning to idle and trying to fuel it for cruise conditions. I had some similar symptoms and wound up replacing my switch, problem solved, but PIA to R&R.
Jim
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From: Texas
Mike V.(Killav) told me that he couldn't hear the throttle switch click and suspected that as well. I haven't delved into that yet.
Of all the things not to replace, how in the world did I miss that? (the throttle switch) Of course, that will mean pulling the intake again, I suppose. Crap, I hate to do stuff more than once!!
Of all the things not to replace, how in the world did I miss that? (the throttle switch) Of course, that will mean pulling the intake again, I suppose. Crap, I hate to do stuff more than once!!
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From: Long Island and Lake George, NY
John,
If it is the switch, I was able to lift the manifold up enough to get at the screws without removing everything. It was tight, but it only took about 2 hours including removing some supercharger stuff.
Don't feel bad about not replacing (or adjusting the rotation/orientation) the switch. I replaced my old functional one with a new bad one! Talk about being pissed!
Jim
If it is the switch, I was able to lift the manifold up enough to get at the screws without removing everything. It was tight, but it only took about 2 hours including removing some supercharger stuff.
Don't feel bad about not replacing (or adjusting the rotation/orientation) the switch. I replaced my old functional one with a new bad one! Talk about being pissed!
Jim
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From: Philly PA
you may be able to not have to pull the intake to fix this .
When you do a intake RnR on an 87 or newer car you should replace both knock sensors, the crank position sensor, the hall sensor, the throttle position swithch, the ISV, the flappy vacuum pot, and every other rubber vent/vacuum line under the intake as well as the O ring for the oil fill tube, and the fuel injection fuel lines and also check the operation of the fuel dampers and the fuel pressure regulator either for holding vacuum or leaking fuel into the vacuum lines
When you do a intake RnR on an 87 or newer car you should replace both knock sensors, the crank position sensor, the hall sensor, the throttle position swithch, the ISV, the flappy vacuum pot, and every other rubber vent/vacuum line under the intake as well as the O ring for the oil fill tube, and the fuel injection fuel lines and also check the operation of the fuel dampers and the fuel pressure regulator either for holding vacuum or leaking fuel into the vacuum lines
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From: theporscheconnection.com
John,
I remember being under the hood and i think we decided that no, we didn't hear the click.
The switch could be bad, if so it should be replaced obviously, but if its good, it could be aligned incorrectly. It is adjustable +/- 5 degrees or so. To adjust or replace you have to pop the manifold up. So its a real pain, but if your doing all that i would just replace the switch anyway. But when you install it make sure that when the throttle body snaps shut it engages that switch.
If the switch does click when you play with the throttle from under the hood, there could be another issue. The issue that i am having is either cable binding, or the linkage binding or something. Ideally when your off throttle the TB should snap back closed, engage the switch that will get the ISV working to stabilize the idle. When i was on the highway and came to a stop on the way up to dallas my car died as well. My ISV and TPS and everything is all new, so cable is the next thing i am looking at and will replace. I will also pull the linkage off the manifold side cover and either disassemble it and fully clean it or just soak it in something to clean out any dirt and they really lube it again before reinstalling. Ive learned that many areas need attention and possible adjustment.
But it sounds like what my car does, but for different reason.
The reason it doesn't die at 2K RPM is that air is still getting through the engine. When the throttle is almost closed it relies on the ISV for airflow into the engine.
Your car idled fine when i heard it, so i do think that heat can play an issue as well as the manifold warms up things expand and something happens. I noticed this on my car too, from cold its never an issue and lately on the trip up it was acting up when the car was warm from the 3 hour drive. Ive been chasing this crap down for 2 years now, it can be real troublesome.
I remember being under the hood and i think we decided that no, we didn't hear the click.
The switch could be bad, if so it should be replaced obviously, but if its good, it could be aligned incorrectly. It is adjustable +/- 5 degrees or so. To adjust or replace you have to pop the manifold up. So its a real pain, but if your doing all that i would just replace the switch anyway. But when you install it make sure that when the throttle body snaps shut it engages that switch.
If the switch does click when you play with the throttle from under the hood, there could be another issue. The issue that i am having is either cable binding, or the linkage binding or something. Ideally when your off throttle the TB should snap back closed, engage the switch that will get the ISV working to stabilize the idle. When i was on the highway and came to a stop on the way up to dallas my car died as well. My ISV and TPS and everything is all new, so cable is the next thing i am looking at and will replace. I will also pull the linkage off the manifold side cover and either disassemble it and fully clean it or just soak it in something to clean out any dirt and they really lube it again before reinstalling. Ive learned that many areas need attention and possible adjustment.
But it sounds like what my car does, but for different reason.
The reason it doesn't die at 2K RPM is that air is still getting through the engine. When the throttle is almost closed it relies on the ISV for airflow into the engine.
Your car idled fine when i heard it, so i do think that heat can play an issue as well as the manifold warms up things expand and something happens. I noticed this on my car too, from cold its never an issue and lately on the trip up it was acting up when the car was warm from the 3 hour drive. Ive been chasing this crap down for 2 years now, it can be real troublesome.
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From: Texas
Mrmerlin,
I did replace the knock sensors, the flappy actuator, the flappy bearings, the hall sensor, the crank position sensor, as well as all the rubber fuel lines, vacuum lines, the gaskets for the oil fill tube, the crossover gaskets and thermostat. It seems as if I replaced everything I could replace except the throttle switch which never occurred to me for some reason.
I will check the fuel pressure dampeners this evening.
I'm headed to 928RUS this afternoon/evening to throw the Hammer on it
I did replace the knock sensors, the flappy actuator, the flappy bearings, the hall sensor, the crank position sensor, as well as all the rubber fuel lines, vacuum lines, the gaskets for the oil fill tube, the crossover gaskets and thermostat. It seems as if I replaced everything I could replace except the throttle switch which never occurred to me for some reason.
I will check the fuel pressure dampeners this evening.
I'm headed to 928RUS this afternoon/evening to throw the Hammer on it
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From: saratoga, ca
having the Throttle switch working, is more likely to cause this issue! I dont run the throttle switch on the race car. (actually, i have a switch for the switch) and only use it on start up, as the idle speed is slightly lower with it working.
in race conditions, and the engine being real hot, the idle switch can kill the engine when it starves it for fuel. removing it, reduces the low rpm braking of the engine by keeping the fuel flowing on decel (at a cost of some mild backfiring, or poping,and even a little flame on race day)
mk
in race conditions, and the engine being real hot, the idle switch can kill the engine when it starves it for fuel. removing it, reduces the low rpm braking of the engine by keeping the fuel flowing on decel (at a cost of some mild backfiring, or poping,and even a little flame on race day)
mk
Throttle switch.
Quick check, pop the hood and grab the throttle linkage. As you move it off the idle stop, there should be a distinct click. If there is no click, it is not returning to idle and trying to fuel it for cruise conditions. I had some similar symptoms and wound up replacing my switch, problem solved, but PIA to R&R.
Jim
Quick check, pop the hood and grab the throttle linkage. As you move it off the idle stop, there should be a distinct click. If there is no click, it is not returning to idle and trying to fuel it for cruise conditions. I had some similar symptoms and wound up replacing my switch, problem solved, but PIA to R&R.
Jim
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From: Texas
Went to Roger's last night and put the Hammer on it. It apparently did not signal the Hammer that it was working, however, Roger did a quick test drive and the MPG went to 90 upon deceleration which Roger says is the sign that it IS working.
We replaced the MAF with a known working MAF and that made some differnce but the idle surging is still there. The ISV checked out fine with the Hammer.
I have not yet checked the fuel dampeners as far as vacuum goes, but will do so this evening.
I did replace the Temp II this morning and will report on that change if any later today
We replaced the MAF with a known working MAF and that made some differnce but the idle surging is still there. The ISV checked out fine with the Hammer.
I have not yet checked the fuel dampeners as far as vacuum goes, but will do so this evening.
I did replace the Temp II this morning and will report on that change if any later today
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having the Throttle switch working, is more likely to cause this issue! I dont run the throttle switch on the race car. (actually, i have a switch for the switch) and only use it on start up, as the idle speed is slightly lower with it working.
in race conditions, and the engine being real hot, the idle switch can kill the engine when it starves it for fuel. removing it, reduces the low rpm braking of the engine by keeping the fuel flowing on decel (at a cost of some mild backfiring, or poping,and even a little flame on race day)
mk
in race conditions, and the engine being real hot, the idle switch can kill the engine when it starves it for fuel. removing it, reduces the low rpm braking of the engine by keeping the fuel flowing on decel (at a cost of some mild backfiring, or poping,and even a little flame on race day)
mk
Did you know that via the SharkTuner you can disable the "fuel cutoff on Decel" or even change the RPM at which it kicks back in. Just thought you'd like to know.