Hello ferrari chatters. I have just finnished a job on my 308 qv. Problem I have is that when I rev the engine, it holds its revs for a moment before slowly dropping. Car ran fine before I did work on it. I've done a cam belt change and also re done my fuel injection lines, new set of injectors and had the plenum off. Accelerator cable is fine, and I can't find any obvious air leak. Am I missing something? Any tips would be much appreciated. Thanks Dean
Check fuel pressure. Check operation electrical fuel pump, cold controle pressure, warm control pressure...
The cable under the carpet is one and the quadrant where the cable connects at the engine might need a bit wd40, thats on the mondial so assume it similar. Enough slack in cable ?
Check the mechanism at the side of the throttle body. There is a sort of roller bearing there & they get stuck. I had one that wore a flat on one side. Doesn't help when that happens. General advice to all: the part is very hard to come by, keep them well greased! Also, check the inside of the TB where the butterfly seats to make sure there is no build up of crap there that is stopping it from closing properly.
Re-done fuel injection lines? Does that include plating work on the steel lines? If, then check if they are partly blocked. I would also check again for vacuum line leaks or misplacing. Best, Peter
Thanks for that. What kind of test would I be doing to check correct pressure? If the engine is running lean, could I simply check the colour of the spark plug tips? White tips = not enough fuel? Cheers.
Running lean is not going to make it keep a higher idle, then drop. Wondering if you have got dirt in an injector when fitting the pipes, doesn't take much. After that might be worth fitting repair kit to fuel distributor if it has no history of being done. About £50 on e bay- id tag on side of distributor head to ensure right kit. i think best to be sure it is returning to the stop when no accelerator, turn it against the spring and let it go, you should hear it snap shut.
Sounds like a distributor advance curve issue potentially. I had a similar issue where the rpms would hold between shifts. Has the distributor ever been rebuilt?
Some years ago I spent 4 hours troubleshooting a Turbo Porsche 911 with similar symptoms to discover it was the floor mat causing the problem...
Thanks mike. Yes spring is definitely snapping it shut. Could possibly be a dirty "new" injector. Cheers
Ok So I got home tonight and had a look at the 308 I can confirm that the throttle body is closing and the carpet is not interfering with the accelerator I still find no obvious vacuum leak.is there a test I can do for a leak? Can someone please educate me on how dirty/blocked injectors or distributor can possibly give the result of holding revs and slowly returning to idle. I would like to get my line of thinking right. The engine is running fine when idling and revving. It does however have a slightly faster idol than previously. Thanks in advance. Dean NZ
Only reason i mention the fuel distributor is that a lot of them have the original internals , diaphagm etc. this controls the balanced volume of fuel to each injector. A friend of mine had severe problems with backfiring/ missing and fuel passing the pistons into the sump- diluted the oil and sump rising- thats the extreme end. The internals of the distributor were shot. For £50 it is worth doing sometime.. if one or more cylinders are getting more fuel and you let off the gas, it might just be burning off the excess in some cylinders. The accelerator cables have been known to stick .
No Can you post a picture of the engine bay, or give the engine family number shown on top of cylinder #1 of the engine block (F...something)? I'd be more suspicious of devices that can allow extra air into the engine (and I would rule those in, or out, initially, by just manually "pinching" or blocking those air hoses), or maybe one of the Digiplex ignition ECU getting stuck at large advance. Not a good sign that you report that the idle speed changed unexpectedly...
On the QV the advance isn't controlled by the distributor, it's done by the electronics. No spinning weights and springs on the QV.
Can you remove the air intake duct and push air flow sensor plate completely down when engine is running.Do this several times and see if plate is returning to initial position without hasitation. Its posible your idle is to high and it gets normal with hasitation. So fuel plunger can be stuck at some point.
Check the brake booster check valve as see if its stuck open. It is connected directly to the plenum.
Hi Steve, my engine is F105A It was a grey market car in the USA. I just looked at a spark plug and it's very black at the tip. One thing I noticed when starting it this morning, was that it started and reved fine when cold. I turned it off and started it 10mins later,engine was warm and it was holding revs again. Cold start was idling at 1200rpm and when I did a warm start it was idling around 1500rpm. Could this be a cold start injector issue? Not shutting off? Just a thought. I did get the injector cleaned and tested during the project. Here are a couple of pics. Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
Sounds like a similar problem I just had but not with my Ferrari. Check the throttle position switch. Might have gone bad. I had the same thing hanging between shifts, and then high idle.
I was chasing an intermittent high idle. Turned out to be crack in one of the cloth covered air lines under the auxiliary air valve. Really tough to see because of the cloth covered lines. As engine moved, the vac leak would get larger or go away.
Not any more (excellent photo BTW). Being imported to the US, it's had quite a few modifications -- VLV removed, frequency valve added, injection ECU added, and I'm guessing the added clump by the coolant expansion tank might be some sort of coolant temperature thermoswitch. That spark plug shows a definite over-richness problem (but that still wouldn't explain the RPM holding high IMO) -- so you probably are faced with confirming the cold and warm control pressures are reasonable and then tweaking the A/F mixture (assuming you've confirmed the cold start injector is not leaking/squirting when warm). Couple basic questions: 1. Is your added frequency valve (the thing with the yellow plastic near the oil filler cap) "buzzing"/vibrating during warm idle? (it should) 2. If you unplug the added O2 sensor during warm idle, does the idle RPM/behavior change significantly? (it shouldn't)
Did you remove the engine for the work that was done? The reason I ask is... That's a LOT of washers spacing forward the rear bulkhead mount on the engine stabilizer bar from the rear cam cover. (5 washers on each side?) My 84 Euro QV (un-modified for grey market compliance) has one washer on each side, that's more than 1/4" difference in the cam cover position between our cars (relative to the rear bulkhead). If you had the engine out, were there 5 washers per side on that engine stabilizer mount? If not, it might be that there's a spacer or two on the engine mounts that weren't re-installed the same way they were when the engine came out? What I'm wondering is if the engine isn't in exactly the same position it was in before the work, then perhaps the throttle cable length needs adjustment to compensate for the shifted position. If you didn't have the engine out, and the stabilizer bar mount always had 5 spacers per side - then never mind! Cheers, Gordon