Hi guys. Its been a while since ive posted here. But ive got a problem I cant figure out. It seems I have aquired what appears to be a common problem with our 420A engines. My Engine rpm's are hanging around 2,000rpm until I come to a complete stop, and it idles around 1,100. Surges to 1,200. Also when idling warm it almost sounds like its miss firing, but its not. Kinda sounds bubbly. Ive changed TPS, IAC. I Checked for vaccum leaks and cannot find any. New upsteam o2. Cleaned throttle body. Butterly closes properly. Found a broken plug wire and changed it, along with plugs and coil but didnt help. No codes coming up at all. It still runs like a scolded dog. My mechanic says its running slightly rich, But nothing to be concerned with. Compression is great. He says he cant find anything wrong with it. Im not sure what to do next. Ive noticed in my searches that in almost all cases there was not a definitive answer, even though there must be. If anybody has actually solved this problem I could use the advice. Im stumped. :scratch

I know this probably isn't the answer the gods would prefer but after a year of hasseling with mine I jb welded my IAC in place and put an idle set screw in the stock throttle body. I have to adjust it from time to time but at least I have control of my idle.

Originally posted by mreigle
after a year of hasseling with mine I jb welded my IAC in place and put an idle set screw in the stock throttle body.

Heh heh, I loves my JB Weld!

MB

Replace the coolant temp sensor.

Originally posted by djtrickee
Replace the coolant temp sensor.

Good call, but Eigle's idea is pretty sweet too. Can't say I've heard of anyone doing that. Wouldn't be too hard, either. Hmmm...

Really. I didnt even think about the CTS.. Ill try that today and let ya know how It does..Ill keep my fingers crossed. Thanks guys...

some years ago I was suckered into one of those ebay miracles. It was a juice box ect sensor resistor. when I installed it I ran it through a switch under the front spoiler so I could turn it off and on. When I did the rebuild, I thought my mechanic disconected it but apparently he didnt. I thought for a minute, Oh yea, Thats it. Any way I yanked that bitch out, Changed the coolant temp sensor, and removed power supply to reset ECU. Smoked a cigg and fired her up...@%$# me..Still the same problem.. Back to the drawing board..Any more suggestions?? :wallbash

Turn the A/C off when you are coming to a stop and the idle is high. See if that solves your problem. My car does the same thing and I noticed that it only did it when the A/C compressor was running. Shortly afterwards I quit caring. It's probably a vacuum leak for something that only works when the compressor is on.

No its not that. a/c on or off makes no differance..

You sure you got the right CTS? There are two, and one only feeds the gauge in the cluster. Replacing that one won't help anything. Just a thought...

Im sure I did. The one you are refering to for the guages is a bit smaller and below the one I changed.....I think.

How about the speed sensor in the transaxle? I haven't had any problems with my speedometer but could it cause problems like this?Maybe Im just grasping at straws.. Any other suggestions??

Here is a pic of my idle set screw.

Joel came up with the idea. If it weren't for him I would sill be cussing at that IAC. First you extend the cone part of the IAC to the point where it is closed then put JB weld on the surface of the cone and then insert.



I had had to adjust it one time in the last couple months. If your idle goes off a little you just tighten or loosen the screw.

Thanks for that Info and picture. Im getting pissed at this point, and that looks like the only good option. Im still baffeled though. Even with a new IAC. There has got to be a simple reason for this problem. I dont know what else to try, other than your idea. Looks like that might be the way to go. If I dont get it soon Ill let ya know how your idea works.

My god what a sexy looking engine... and i cant even see the whole thing. I think i'm gonna give this a shot too when i get the new motor in.

You can always test it by turning the IAC until it is closed and inserting it back into the throttle body. They insert a set screw. If it works for you take te IAC back out and JB weld it in place. If you are patient you can take the IAC off without removing the throttle body.

It worked for me and gives me control of my idle for the first time since I built the engine.

First I have to agree with red. That motor looks damn sweet. I thought mine looked good. I would have never thought you could get the IAC off without removing the throttle body. I assume you have. I just hate to do that to one I just bought last week. I already tossed the old one like a dumb ass.

Once again you can take out the IAC and just unscrew it manually until it closes the passage way. Don't connect the harness to the IAC and it will stay that way. If it works and you don't JB weld it then the vibration of the vehicle will make the IAC turn enough to open the passage way again and throw off the calibration with the set screw.

Thanks for the props on the engine. It has looked better before but I have just been working on tuning that last year. I need to get my turbo upgraded and some more ceramic coating redone soon. I also need to repolish the outside of my head.

I got a couple things for ya to try - as you shouldn't have to screw with your IAC if it's new. first (dumb remark) make sure you don't have a vaccum leak... Our cars keep idle up (1200ish) until we're stopped to create more vaccum for breaking, so make sure to check your power booster for leaks. Pull the hose off to it and plug it, if anything. Also check your exhaust system - a plugged cat/muffler sometimes will make rpm's do REALLY strange things. Usually it only makes the RPM's return to idle VERY slowly. Maybe test if with open header if a shop'll charge ya to check it. I doubt it's that as you said it still runs great, but nevertheless... I've had mine stick like that a couple times, but a pop of the throttle and it reset - I think i just had crap in my TB though... Your MAT and CTS check out okay - not acting like it's still tryin to warm up the engine?

Checking vacuum lines would be a given for idle issues.

It didn't help for my ride.

Well at this point I'm gonna go back through my vaccum lines one more time. Maybe I missed something. If I did its a small leak. Didnt I see a posting for all the vaccum lines on on our cars here somewhere?

They all come off your intake manifold except for your evap which come off your throttle body.

Any update on this?

As a matter of fact yes. I went through every vaccum line in the car and couldnt find a thing. Replaced most I could get to. I finally gave up and brought the car to a totaly different mechanic than the one that built the motor for me. He says its the intake manifold leaking. I did notice I could all but completely cut off air to the throttle body and it didnt make much of a differance.What pissed me off when I called my regular mechanic he says he suspected it. If you saw in an erlier post he had the car for 2 days and said he couldnt find anything wrong with the car. the motor only has 20,000 since he rebuilt it. I wouldn't have thought it would be leaking. I think he was hesitant to say they f%@?ed up. I dont know. I do drive the hell out of it. Its my daily driver and I drive it 70 miles a day to work and back 5 days a week..Mostly highway..Cruising..80-85-95-100..Ive been driving the same road for 20 years now and I have to say, since ive had this car, Ive still enjoy the ride. Anyway tomorow I get it back.. we will see..Hes charging me $125..For me. Thats a bargan. I dont have the patients to be a mechanic and I dont claim to be one. Hats off to all you guys who rip your motors down and rebuild them in a weekend..:bowdown I just like to drive em..Ill post back tomorow when I get it back.

It takes me much longer than a weekend to tear my motor down but I guess I am one of the slower ones on the board. Usually it takes me a few weeks because there are always small things I kept putting off until I tore it down again.

Keep us posted on the location of your leak. Idle issues plague many with our engine.

you could do the spray starting fluid test, see when the idle raises. helps if you have the little tube to spray with, better aim to pinpoint area. That is if you didn't have the other mech. repair it.

Well everyone that was it.. Inner intake manifold gasket. They did a smoke check and they said it was blasting a stream of smoke out of the area of #1 and #2 cylinder intake. Apparently there are 2 gaskets?? An inner and outer. Not sure what he was meaning, he called it something but I was so glad to get it back, I forgot. Stupid me.. He said the outer one was soft and pliable but the inner one was cracked and broken. He also said there is no way it got so bad in 20,000 miles. He said either it wasn't replaced when the motor was rebuilt OR it was "badly defective". He followed that with he didnt want to talk bad about a fellow mechanic.Humm!
Yea..I bet! Anyway shes back on the road and running fabulous. Idles right at 750-800 rpm. Just like the old days.Thanks to everyone for your input with this problem. Ive always been able to count on this site. Even if at times its just for moral support or someone who can relate...That being said... Im good here!! :cheers

Glad to hear everything worked out.

Originally posted by damooch
Well everyone that was it.. Inner intake manifold gasket. They did a smoke check and they said it was blasting a stream of smoke out of the area of #1 and #2 cylinder intake. Apparently there are 2 gaskets?? An inner and outer. Not sure what he was meaning, he called it something but I was so glad to get it back, I forgot. Stupid me.. He said the outer one was soft and pliable but the inner one was cracked and broken. He also said there is no way it got so bad in 20,000 miles. He said either it wasn't replaced when the motor was rebuilt OR it was "badly defective". He followed that with he didnt want to talk bad about a fellow mechanic.Humm! Yea..I bet! Anyway shes back on the road and running fabulous. Idles right at 750-800 rpm. Just like the old days.Thanks to everyone for your input with this problem. Ive always been able to count on this site. Even if at times its just for moral support or someone who can relate...That being said... Im good here!! :cheers

Guys Im sorry for that ignorant explanation. I really didnt know which gasket he replaced myself so I called him back today. He told me it was the gasket along the plenum. There is no inner gasket..DUH!!

Originally posted by damooch
Guys Im sorry for that ignorant explanation. I really didnt know which gasket he replaced myself so I called him back today. He told me it was the gasket along the plenum. There is no inner gasket..DUH!!

No worries, mooch.

We knew what you meant. Stock manifold is a 2-piece design. Typically referred to as upper and lower manifolds. There is a gasket at the head and another between the upper and lower halves. A leak in either of them is no different than a leaking vac line somewhere off the plenum.

Glad to hear it's all better now. As a concession to the buddy who put the new engine together for you, if you don't separate the two halves, why replace that gasket? They're fairly robust. Obviously, if a leak in that location were common, someone might have suggested that gasket in particular.

Cheers.

Originally posted by DR1665
As a concession to the buddy who put the new engine together for you, if you don't separate the two halves, why replace that gasket? They're fairly robust. Obviously, if a leak in that location were common, someone might have suggested that gasket in particular.

Zat eez correct. I never replace that gasket.

I agree. After I spoke to the guy who did the work, and I realized where it was leaking, I thought the same thing. I thought it was leaking along the head. I know that one is new. My bad Mr. Mike. (my mechanic).