after engine swap .. RPMs skyrocket on ignition
 

weird, right?!

here's the story:
i got a rebuilt 1997 engine into the 1995 body. using the 1995 wiring , cas, intake manifold, coil pack and fuel feed rail. also have installed is the FMII with the 1997 oil feed line. engine management is a megasquirt that was working without issue when the 1995 engine was in the car, tuned with the FMII system. fuel injectors are 550cc ones from FM.
so everything is installed.. i checked lines, vacuum tubes, piping, wires.. everything .. over and over as much as i can.
i am able to start the car.

here's the problem:
immediately after starting the car, the RPMs sky rocket, and keep climbing. i get freaked out and shut the car down shortly after (between 4000-5000rpms). i did this a couple times.. all with the same result. it's as if the throttle is stuck open or the accelerator pedal is being floored. however, neither of this is the case. the pedal is not being touched, nor is it stuck. the throttle cable itself is loose and the flap it controls is closed.

this is where i'm stuck.. i have absolutely no clue for what can cause this issue. and because of that, i have no idea where to start troubleshooting!

i received a suggestion that an o-ring around an injector blew and it's causing a vacuum leak. i looked at those, and they appear to be fine. i did notice though, that the fuel rail was a bit tight.. enough that i couldn't rotate the fuel injectors at all. so i loosened the rail a little, but got the same result when starting the car. (slightly off topic question.. is the fuel feed rail for the 1995 and 1997 engine the same?) based off the idea of a vacuum leak .. i rechecked all the vacuum lines .. in the engine bay and the lines to the LC-1 gauge and megasquirt... but all are snug and connected. though .. i don't really see how this can be the problem because i've pulled a vacuum line off before while driving and it didn't make my RPMs skyrocket to redline.

soooo .. this is where i'm stuck .. have any helpful ideas or suggestions on what can cause the RPMs to skyrocket immediately after starting the car?!

Have you tried starting it with your IAC valve intake blocked off?

i'll give that a shot today... what's a good way to block it off without risk of sucking anything into the engine?

I'd do a boost leak test for the hell of it, but I don't think that's the main cause. Were the injectors tuned via the megasquirt before you put this engine in?

yes. injectors were tuned in megasquirt using the 1995 engine prior to the engine swap.

how do i do a boost leak test?

has anyone come across engine behavior like this?
what are possible causes?
bad timing job?... vacuum leak?... bad tune in megasquirt?... megasquirt thinking the timing is very very different than what it actually is?... injectors dumping too much fuel?

Sounds like the idle settings on the old system don't work for the new system. Try retuning idle settings.

i'll give that a try after work.

but if it is the case .. why will the RPMs climb into redline? should it stop climbing and idle at a steady, but higher RPM?

I doubt it's the MS settings. Did you forget to plug the brake booster or pcv line back in?

what or where is the brake booster?

pcv is plugged in.

could this be because of a bad timing job?

also .. where is the IAC valve?

oh ... another thing to note.

The car previously had PS and AC. I removed both of those. But didn't make any changes to megasquirt (didn't think i needed to). Also.. the wires/plugs going to both AC and PS are now left dangling. Could this cause an issue? something needs to be grounded?

the large line that runs from the master clyinder to the back of the intake manifold. There is also a random vacuum port on the back of the intake manifold that should have a rubber nipple on it, possibly came from an auto motor and had none? look at your old motor to see what I'm talking about.

bad timing job, no way, if anything rpms would suffer. increases RPMs = increased airflow, something is letting too much air into the motor.

IAC is the idle valve bolted to the throttle body.

the large line that runs from the master cylinder to the back of the intake manifold .. is that a metal line?

the random vacuum port on the back of the intake manifold still has the rubber nipple on it. i am using the 1995 intake manifold on the 1997 engine.

at least this makes me feel a bit better about the timing job . .haha .. wasn't sure if i did that correctly!

so i'm searching for massive amounts of air entering the intake .. at least this is a good start for my troubleshooting.. thanks!

more on the IAC .. is the setting for that the same as the bolt that i screw in/out to adjust the idle speed?

Do a google search on a boost leak tester, get a compressor or hand pump, and pump air through your intake to find any leaks.

I had a similar issue recently when I swapped a 3.0 Eclipse motor in my wife's 2.5 Sebring. Turned out when I reinstalled the intake, manifold, I had a hose between the manifold and heads, in essence introducing a massive intake leak. The RPM shot through the roof when I started the car.

son of a bbbbb
 

gahh .. i think i found the issue.

Did you know .. the 1995 intake and 1997 intake are slightly different?!
the studs line up the exact same .. but the ports on the 1995 intake are slightly lower than the ports on the 1997! and because of this, there is a little gap by each port to the engine. sooo .. i guess this is where my leak is that is allowing MASSIVE amounts of air into the engine.

Pics attached... yay?!

Attachment 189905

Attachment 189906

so .. now the next step .. how do i fix this? currently i'm using a 1995 metal intake gasket. i do have a 1997 metal intake gasket .. and it looks like it will just barely cover up the gap .. is this ok to do? or is there another action/remedy that is better and more advised?

though .. i must thank all of you for responses and ideas. gave me something to look for and led to finding the gap!

IIRC 95-97 are the same right?

Are you sure the throttle body butterfly plate isn't held open somehow?

You can confirm any vacuum leak using "flammable" brake cleaner in the areas you pictured, but you have to have the car running. The engine will stumble if you spray it into a leak.

yep ... that thing flaps and closes without issue.

i thought the 95 and 97 engines are supposed to be the same too .. but apparently not that much in my case...

in the picture below .. i circled in red where the gap is.
i have identified this as a gap by placing a folded piece of paper into the gap .. and it goes in.. ugh.

then .. i located the 1997 metal intake gasket and placed it on the 1995 engine i have lying around. the stud holes matched perfectly .. but the gasket port holes sat higher than on the actual engine. so this backs up my idea that there is an actual gap here.

Attachment 189904

soooooo ... what do i have wrong here?! and what can i do now....

i'm not sure if using the 1997 metal gasket will be a good fix because that is indented ... and trying to squeeze it into place between the 1995 intake and 1997 engine may not seal correctly?

Even if the gasket doesn't come to the edges, the surfaces should seal. Was the '95 gasket reused?

yep .. oops .. 95 gasket was reused.

see, that's what i thought about the surfaces. clearly with my setup now, the 95 manifold and 97 head surfaces do not match up! is that ... really bad?