Engine roars up to 1.5 rpm on cold start, is this normal?
When I first fire mine up, I don't touch the gas pedal or move the car at all until it settles back down to a normal idle.Yes. Normal. As far back as I can recall back at least to my '96 Mustang, upon engine start the engine RPMs "zoom" up to about 1.5K then drop to a faster than normal idle speed for a while. With some cars the fast idle drops to normal idle speed when the secondary air injection system shuts down and the engine controller is able to go into closed loop mode.
The engine speed initially goes up to help ensure the gear oil pump primes and to get oil flowing to the engine ASAP. Gear pumps are not very efficient at slow speeds and the engine starter probably only cranks the engine to around 75 RPMs. It only takes one cylinder going through a good intake/power stroke to get the engine running. (Any one who has kick started a motorcycle engine and I kick started a number of different engines from a 90cc dirt bike to a 1000cc Harley Davidson Sportster) knows it just takes one good crank to get the engine running.)
Additionally the higher RPMs help ensure the residual oil in the bearings forms a hydrodynamic bearing (a wedge of oil) that prevents metal to metal contact. This residual oil suffices until the oil from the gear pump arrives.
Normal but important. Generally I let the engine idle until the RPMs drop. This is a sign -- as I touched upon above -- the engine controller is in closed loop mode and is able to more precisely fuel the engine.
To some extent but the converters are heated up mainly because the engine controller supplies excess fuel and the air injection system injects air into the exhaust to provide the air needed for the rich exhaust mixture to burn in the exhaust and this supplies extra eat to get the converters hot quicker.It’s to heat up the cats quickly and it settles down shortly after. All new vehicles do it.
Its the only reason I’ve been given as an answer to this question and the same answer I’ve seen in any forum when the subject arose.To some extent but the converters are heated up mainly because the engine controller supplies excess fuel and the air injection system injects air into the exhaust to provide the air needed for the rich exhaust mixture to burn in the exhaust and this supplies extra eat to get the converters hot quicker.
Don't hear this so much -- in fact I don't think I've ever heard it -- with my HC or JCW but with my 996 Turbo I'd hear faint backfires from the exhaust system during when the RPMs were elevated.
The converters heat up pretty quick as do the O2 sensors. Occasionally I'd monitor the OBD status with my OBD2 reader and concurrent with the RPMs dropping the secondary air status would switch from downstream to atmosphere (essentially it would shut off) and the OBD status would switch from open loop to closed loop mode. This was an indication the O2 sensors at least were up to temperature. The converters were probably up to temperature too as the #2 sensor readings were as I expected them to be, signaling no excess oxygen in the exhaust from the converters. A sure sign this oxygen was being consumed in the converters.
I hear ya! And so do my neighbors! I leave for work at 6am and its still dark and calm out. Everyone of my neighbors know when I left for work. Sometimes I forgot to close my cut outs from the night before and I can't close them fast enough.!!