Forum:
I own a 93' Sportrak (Feroza) HD-E, and i recently installed a new Thermostat. Ever since when i start her up she idles fine, when i take her out and she starts to warm up and i put her in neutral she revs up to one and a half revs then drops to one continously which gets a bit annoying when i am sat at traffic lights as i must appear like a boy racer just reving my engine for kicks.
I have had a play with the idle speed but this has no effect, there also does not seem to be any loose hoses. What i have noticed is i can make it worse by turning on my air con, this increses the revs and the speeds it up. I think it may be haunted.
Any advice would be greatly appreciated.
Thanks. Ant.
The revs will go up when you
The revs will go up when you turn on the air con. It's suposed to do that, so the engine doesn't stall from the extra load as well as to provide the extra power to drive the pump.
You other problem (If it's an injected engine) could be the air bypass tube in the throtle body is getting blocked. This would couse the rev.'s to drop off a tick over(when the butterfly is totaly shut), the ECU reaslising the engine is staling opens puts the rev.'s up. When the butterfly opens a little there is plenty of air so the engin runs fine, and the ECU lets it go back to tick over, the b/f shuts again and the cycle repeats. This can couse the engine rev.'s to 'yo-yo'.
This can sometimes be coused (in cold weather) by ice crystals forming in the bypass tube as the engine runs, and the cold air rushes through the throughtl body. Cleaning this tube out, and macking sure it's dry could solv your problem.
Any veiws expresed in this thread by me are purely from my own experience, and (sometimes) falible memory. Hope my comments help, but please don't take them as gospel.
thank you all
hi i found this thread after weeks of pulling my hair out. being the owner of an over reving and hunting sportrak your advice got the job sorted in under an hour (blocked water pipes)many thanks to all involved
If you ever suspect the
If you ever suspect the faulty air bypass part of throttle body, a quick easy test is remove the hose onto throttle body, have engine running, then stick your finger over the small hole inside the neck of throttle body before the butterfly flap, to seal up the bypass.
Any excess idle speed/hunting caused by that being faulty will instantly stop.
Sorry i have just repeated
Sorry i have just repeated what Mark wrote!
I think we've got it
Top Man Nev.K.
I checked the Auxiliary Air valve and that was ok so i moved on to the Air Bypass Tube, i believe i got the right one, (it runs from top of the engine block to the top of the throttle body, by the main air intake). Anyway the hose was full of black crap im guessing from the engine so cleaned out the hose and the hose connectors on the engine block and the air intake. Started her up and all seems well, increased the revs with the idle screw which before would kick in the 'yo-yo' revs, but now she purrs normally.
Thanks a million for your help, gonna go give her a proper run around to be sure.
Ant.
That's not the hose I ment.
That's not the hose I ment. But it could be the problem, as luck would have it. That sounds like the pipe which takes the fumes out of the rocker cover and putes it back through the engine, to burn it. If that is full of crap, it could be putting the crap through the throtl body and lousing it up. The tube I was refuring to is part of the throtle body itself. It will be a small hole in the molding of the body which opens out either side of the buterfly, or even just a hole in the buterfly itself.
Any veiws expresed in this thread by me are purely from my own experience, and (sometimes) falible memory. Hope my comments help, but please don't take them as gospel.
I Spoke too Soon
Took her out for a spin and she started playing up again, still got the yo-yo's. The wrong hose, bugger. I have a maintenance manual i got online but it does not identify individual parts. Will have a look for the hose/hole in the butterfly, but first the butterfly, is it the bronze coloured circular piece about 2 inches wide that looks like it controls the clean air intake, past the hole for the auxiliary air valve and the hole for the hose i mistook the bypass for.
Thanks again for your time, Ant.
Sounds like it, from your
Sounds like it, from your description. Basicly the big (probably brass) part that opens and closes ,by revolving around its centre, across the air intake in the throtal body when you push the loud peddle.
Any veiws expresed in this thread by me are purely from my own experience, and (sometimes) falible memory. Hope my comments help, but please don't take them as gospel.
This is what is really happening....
Ant,
The problem you have is that the Air Bypass Valve (ABV) is probably not shutting completely. The ABV is located on the underside of the throttlebody (as part of the casting) and causes the tickover RPM to be increased when the engine is cold. It does this by sensing the temperature in the water system (via the two water pipes connected), when the engine heats up the ABV correspondly closes therefore shutting off this air supply. When fully warm the valve should be completely closed and the tickover RPM will be controlled by the idle screw. The tickover can be slightly incresed by switching on either the lights, heater blower, rear window demist or air con. This increase is controlled by the VSV mounted just right of center of the bulkhead (has two black pipes attached) and ensures the alternator can put out a little more power when the above devices are turned on.
The Yo-Yo effect.
What is happening here is that firstly the ECU correctly detects that the engine is fully warmed up and therefore expects the tickover RPM to be below about 1100 RPM. With the ABV malfunctioning and causing the engine to rev to about 1500 RPM, the ECU thinks the engine is in an overrun condition (see below). This is because the throttle position sensor switch is telling the ECU that there is no throttle input (throttle butterfly valve closed) and correctly shuts off all the fuel injectors until the revs drop to below about 1100RPM at which point they fire up increasing the rev up to 1500 again.
This cycle can be broken by removing the connector to the throttle position sensor, the ECU then thinks the throttle is partially open and maintains the correct injector signals therefor keeping the RPM constant at about 1500.
Overrun condition - using the engine to slow the vehicle when decending down a hill or stopping for a junction. In this condition the ECU stops the fuel injectors to save fuel. The injectors restart when you either 'put your foot down' or the engine reaches tick over revs.
The Air Bypass Valve (ABV) can be easily checked. When the engine is fully warmed up remove the air filter ducting to the throttle body so that you can see into the throttle body. You will see inside just in front of the brass butterfly valve at the bottom an oval hole about 12mm diameter. Start the engine, at which point it will be ticking over at a high RPM and possibly yo-yo-ing, put your finger over this oval hole and observe the engine response. You may feel your finger being sucked into the hole.
If the RPM doesn't change then there is an air leak somewhere else on the inlet manifold.
If the RPM drops to a normal tickover and the yo-yo-ing stops then the ABV is malfuncting and not shutting completely.
If from above the ABV is at fault then check that the alloy casing around the pipe connections on the throttle body is hot. If it is not hot then hot water is not getting through from the engine, either a blockage in one of the two pipes or an airlock in the waterway in the throttle body. Check the pipes and/or bleed the air out.
If it is hot then the ABV is faulty and the throttle body will need replacing.
Hope this explanation shows what is really happening
Cheers
Mark
NE Hants
pulling my hair out!
pulling my hair out!
Update
Right here is what i have done so far on the Beast. Spent my night shift removing the throttle body and checked all the tubes and holes and they are all fine. Checked the pressure sensor and the throttle position senor and they are ok. Not too sure about the oxygen sensor though, but would this effect it in that way?
Here is the state of play with it now, starts up fine but idles at about 1.5 even with the idle screw fully in, when she starts to 'yo yo' rev i have managed to get it to stop by unplugging the throttle position sensor but the high idle revs remain.
Really bafled now, not too sure where to go with it. Wondering if its getting too much juice somewhere or if its the ecu?
Any help would be much appreciated, cheers, Ant.
I had this problem with my
I had this problem with my '94 sportrak about 6 weeks ago, the engine would be fine when starting it, but as soon as the warm up cycle had finished (most noticable after driving a mile then pulling up at the traffic lights) the engine would yoyo.
Turns out both the radiator and reserve bottle were nearly empty, I didn't notice until it'd completely run out and the engine was overheating.
Filled them both up to the top with a 1:1 mix of water and coolant and it's back to normal
Jason "Foxdie" Gaunt
--
Jason "Foxdie" Gaunt
Could be a vacuum leak
Mine was hunting - at slightly higher revs than yours. It was running at about 1900rpm at tickover and then once it was warm it was hunting between 1500 and 2000 ish. It had lost a vac hose on the power steering pump, put it back on and all good.