Göran W Posted August 16, 2015 Report Share Posted August 16, 2015 Eldo -90 4,5. Got a strange problem. Engine adapts to any speed and keeps the speed (on flat road) if take my foot of the accelerator. Must use brake to reduce speed. It then adapts to the "new" speed and keeps it. This has nothing to do with cruise control (CC off). It is based only on revs - not speed. If I use CC it will keep the speed on flat road or uphill but no brake downhill so car just speeds away........ At start the engine revs up but soon gets to normal idle at 650-725 rpm. If I brake to full stop idle gets normal. What is this? No codes that gives a clue! Link to comment Share on other sites More sharing options...
cdgrinci Posted August 17, 2015 Report Share Posted August 17, 2015 If on this same flat road, and say an even 50 mph (or whatever), and then you 'pop' the tranny into neutral, what happens to the rpms (then)? I would start with cleaning the throttle body; maybe carbon slowing the return to idle position. On a flat road with low requirement for engine torque it would take relatively low power to maintain an elevated rpm thus appearing to match engine speed to vehicle speed. Just a guess (and I would look for vacuum leaks as well). Chuck '19 CT6, '04 Bravada........but still lusting for that '69 Z-28 Link to comment Share on other sites More sharing options...
Göran W Posted August 17, 2015 Author Report Share Posted August 17, 2015 Thanks. Sound plausible if it wasn´t for the fact that flat road followed by uphill and then flat road again - it retrieves it original speed. Must use the brakes to permanently lower the rpm. Link to comment Share on other sites More sharing options...
KHE Posted August 17, 2015 Report Share Posted August 17, 2015 Possibly, the idle speed control motor acting up? Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
rockfangd Posted August 17, 2015 Report Share Posted August 17, 2015 Possibly, the idle speed control motor acting up? I was thinking the same. Fairly common failure item IIRC. Definately check the throttle body though. Carbon slows the movement and can hold it open/closed GM FAN FOREVER Nice, clean, luxury= fine automobile Link to comment Share on other sites More sharing options...
Göran W Posted August 17, 2015 Author Report Share Posted August 17, 2015 Thnx guys! Best manor to clean TB? Link to comment Share on other sites More sharing options...
KHE Posted August 18, 2015 Report Share Posted August 18, 2015 Throttle body cleaner and a rag. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
airmike Posted August 18, 2015 Report Share Posted August 18, 2015 Just don't let it pool in the intake. You don't want to hydro lock. Make sure to get it all soaked up. Not a bad job. Link to comment Share on other sites More sharing options...
Göran W Posted August 18, 2015 Author Report Share Posted August 18, 2015 Throttle body cleaner Just what is "Throttle body cleaner"? I have only seen it mentioned here but never in Sweden. Link to comment Share on other sites More sharing options...
cdgrinci Posted August 18, 2015 Report Share Posted August 18, 2015 Just what is "Throttle body cleaner"? I have only seen it mentioned here but never in Sweden. It is similar to carburetor cleaner, which is too harsh and can harm intakes that have a coating (for enhanced airflow), sensors and seals. Whatever you use, make sure it says it is safe for intakes. Chuck '19 CT6, '04 Bravada........but still lusting for that '69 Z-28 Link to comment Share on other sites More sharing options...
rockfangd Posted August 20, 2015 Report Share Posted August 20, 2015 If cleaning with TB installed I use intake cleaner. If removed I use TB cleaner GM FAN FOREVER Nice, clean, luxury= fine automobile Link to comment Share on other sites More sharing options...
Göran W Posted August 20, 2015 Author Report Share Posted August 20, 2015 Thnx! Link to comment Share on other sites More sharing options...
barczy01 Posted August 24, 2015 Report Share Posted August 24, 2015 TPS and ISC retracted and extended adjustments are a chore on these cars. If the ISC arm is adjusted too far out it will give you a run on condition. Plus, after all the fun of setting up the ISC, TPS and cleaning the TB, you get do do an idle learn. Link to comment Share on other sites More sharing options...
KHE Posted August 24, 2015 Report Share Posted August 24, 2015 Adjusting the ISC is straightforward - there is a procedure in the archives. The ISC adjustment does not drift or get out of adjustment. If the ISC si ratcheting, it is most likely the closed throttle switch contacts in the ISC assembly. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
Göran W Posted August 24, 2015 Author Report Share Posted August 24, 2015 I take it must do this after disassembling TB for cleaning or? Link to comment Share on other sites More sharing options...
barczy01 Posted August 25, 2015 Report Share Posted August 25, 2015 Disassemble? Clean out the egr tubes on the bottom of the intake and throttle blades in the bores of the throttle body. Link to comment Share on other sites More sharing options...
Göran W Posted August 25, 2015 Author Report Share Posted August 25, 2015 Thnx! Link to comment Share on other sites More sharing options...
Göran W Posted August 26, 2015 Author Report Share Posted August 26, 2015 Found a small air leak in the gasket on top of TB. Relevant? Link to comment Share on other sites More sharing options...
cdgrinci Posted August 26, 2015 Report Share Posted August 26, 2015 Depending on severity, Yes, because it is un-metered air (and can/will cause a lean condition); fix it and see if it helps. Chuck '19 CT6, '04 Bravada........but still lusting for that '69 Z-28 Link to comment Share on other sites More sharing options...
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