Lately and consistently, while I am driving at speed my tach will drop violently 500+ rpm but instantly shoot back up to the correct speed… at first I attributed this to bad gas as the car had been sitting for 5 months (with stabil fuel stabilizer) but now im 4-5 fresh tanks deep and it is happening more than ever. I’m concerned the car will die while I’m driving, and even if it doesn’t, this can’t be healthy… any ideas?
try fuel injector cleaner.
check for codes. sounds like possible crank sensor. which should set a code. but then again, could be a lot of things. check for codes
Check your distributor (ignitor component). Can you rev the car when the RPM’s drop or does nothing happen when you hit the gas? If nothing happens then I think its the ignitor. This will not give you a code if it’s this problem.
Try the suggestions everyone else posted…but I’m suspecting that your Exhaust system might be getting clogged …If the suggestions post by everyone else does not apply…Try disconnecting your down pipe from your manifold I know this is goin to be loud but try to see if your RPM will stablize if it does replace your cat and remove your resonator also check your muffler and make sure its not clogged as well…
I ran into this problem before
wish you luck.
[QUOTE=zoomxjoe;2158871]Try the suggestions everyone else posted…but I’m suspecting that your Exhaust system might be getting clogged …If the suggestions post by everyone else does not apply…Try disconnecting your down pipe from your manifold I know this is goin to be loud but try to see if your RPM will stablize if it does replace your cat and remove your resonator also check your muffler and make sure its not clogged as well…
I ran into this problem before
wish you luck.[/QUOTE]
you can also try testing with a vacuum gauge. vacuum will rise and drop to 0 consistently if the exhaust is being forced back
Is your car a manual or an automatic? If its a manual then its an electrical problem. Its not possible for a manual to just drop 500rpm and regain it within a second.
The car is a manual. I highly doubt that the exhaust is clogged, as its a 1 year old ex-mag with a 2 year old cat-co high flow converter; also the problem is too random and erratic to be something I could imagine as an exhaust issue
Not to thread jack, but I just had a similar problem last night. Tach dropped to nothing, and when I tried to give it gas, it just kind of… lurched, and wouldn’t accelerate for no more than 7 or so seconds, then it finally took off just like nothing had happened. Mechanically, the engine is as strong as it can be, compression is great, idle is fantastic. But when I stopped it, and opened the hood, I saw some gas leakage from the exhaust manifold flange (Old gasket, need to replace it anyway) I think it’s safe to assume it’s an electrical or perhaps a fuel problem?
Car was sitting for many years, I drained the old gas, but I think I forgot to stick some injector cleaner in there. I should probably change the filter too. But since I saw the fuel there, it made me think it lost spark or something for a bit, and just chucked out some fuel.
Any ideas? And again, sorry if this is a thread jack, but I felt my problem was a bit similar.