RPM surging... need some help

JoeyLincolnMK8

JoeyLincolnMK8

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Ok guys, first off let me say that i have pretty much done all i can do to try and resolve this issue. the problem is no matter what RPM and MPH, the rpm's will surge to anywhere from 2500 to 3k.

the items i installed trying to fix this issue are...
1-2 springs + mercon V
new MLPS
3200 stall converter and replaced oil pump seal for the tranny and rear main. with a another flush or mercon V.
full tune up... plugs/wires

i honestly believe it could be my PCM needing to be reflashed. or a vaccum leak could be causing this? i really need some help here, i have been reading a lot of posts that tranny swaps and or rebuilds have not resolved certain issues. so i need to ask the mark VIII guru's. i appreciate it guys!
 
Hope it's not the dreaded IAC valve, Gen.1 is a real pain, Gen.2 probably 5 minutes. You probably checked it already but does it do it all the time, or just with the air on? Could just need a charge, hopefully it's something simple.
 
well im ordering the thing anyway. i hope that is it. i did drive the car for a good length of time w/o the ac on. and it still did the samething. however i do notice that when it is in gear for awhile just about when it is going to shift, that is when it surges! effin strange. need more insight guys!
 
personally, I vote for the vacuum leak-if you have been removing and installing lots of stuff, that's the ticket, might be something small you overlooked, or thought was connected when it wasn't, or maybe a cracked line (we all get them, don't we?)-get out the handy spraycan of whatever and go to town-at least you'l know it's NOT that, but that's what it sounds like. I wouldn't wish an IAC Gen 1 replacement on anyone, and I would (and have) tried anything else first.
 
yeah i do notice w/ the high stall converter my shift points are totally different. but i can tell you, it is def not caused by the stall converter. before i replaced the TC. i was getting a "big bang" feel after it surged and then down shifted. so soon after i installed the stall converter. i was getting the surge again, but this time no "big bang" feel but, it felt like the car was jerking forward to get into the next gear. so then the other day i replaced the MLPS. seemed like all was good for a day or so, then i got the surge again. no jerking, no big bang. it is very hard to explain typing it up. i am going to try and video it. but i hope my explanation is good enough.
 
just finished replacing the IAC valve and the RPM still surges alil. however the main reason for replacing the IAC is that, ive been getting a rough idle where the RPM bounces between 500-650rpms. and this mainly occurs w/ the ac turned off!!! the problem still persists where the rpm's are jumping w/ the ac off. idle does not feel rough like it was before, so could this problem be the TPS? before i replace that i am going to try to clean the MAF sensor. ill let you guys know, but any idea's would be greatly appreciated!
 
Do you mean that while you're sitting at a stop light, the car is jumping up to 2500-3000 RPMS, or that when you're driver at around 3000 RPMs you can feel it bouncing around between 2500-3000 RPMs?

Because if this is while the car is moving, I'd also look into the IMRCs. They could be leaking.
 
ok...lol, maybe i need to explain my issue alil better. the boucing of rpm's occur only when at a stop or just sitting in park w/ the ac off. now for the surging this typically happens at random, the jump in rpm's is very small, usually like 200 or 300 more. lets just say, i am driving doing 65 or 70 and my rpms are at 2200, it would surge around 2500.
 
I don't know if this is the same situation or not but my 150 had a problem where the rpm's would stay high in it. I have a stick so if i pushed the cluth in it would shoot up to 3000 and stay their. so every time I would shift the rpm would surge on me.So if you had the same problem you wouldn't notice as much of a increase as I did because you have a constant load on your trans.

I replaced the IAC and throttle postion sensor and it went away. Also I get a small rpm surge of 200 to 300 at idle, but It's done that since it was new, they told me thats the compressor cycling on the truck. I Also put a oil seperator inline to keep it clean up top.

Maybe check for any cracks or leaks in you intake hose, I know a little air getting in behind the MAF will cause it to surge also. I have no idea what effects you get from a dirty TB. Make sure you replace your gasket when you clean it.

Did you put a new gasket on when you replaced your IAC?
 
Spray some carb cleaner or something around the intake manifold, see if the stumble gets worse.
 
i dont understand your suggestion. spray carb cleaner around the intake manifold to see if the stumble gets worse. what are you suspecting that it is?
 
I think he is refering to that if you have a air leak on the top half of the engine it will suck the cleaner in and run rougher. This lets you know that you have a air leak.
 
JoeyLincolnMK8 said:
i dont understand your suggestion. spray carb cleaner around the intake manifold to see if the stumble gets worse. what are you suspecting that it is?
Click to expand...

If it's sucking in air (through a vacuum line, a bad gasket, a seal) it'll often misfire when it sucks in the spray. Sometimes it can help you locate seemingly invisible problems.

For example, the rear of my IRMC is leaking from the shaft, when I spray in that area, the engine misfires. If it weren't leaking, there'd be no effect.
 
JoeyLincolnMK8 said:
ok...lol, maybe i need to explain my issue alil better. the boucing of rpm's occur only when at a stop or just sitting in park w/ the ac off. now for the surging this typically happens at random, the jump in rpm's is very small, usually like 200 or 300 more. lets just say, i am driving doing 65 or 70 and my rpms are at 2200, it would surge around 2500.
Click to expand...

How did you go about tackling that IAC job? It looks so damn difficult and hard to get to.
 
JoeyLincolnMK8 said:
ok...lol, maybe i need to explain my issue alil better. the boucing of rpm's occur only when at a stop or just sitting in park w/ the ac off. now for the surging this typically happens at random, the jump in rpm's is very small, usually like 200 or 300 more. lets just say, i am driving doing 65 or 70 and my rpms are at 2200, it would surge around 2500.
Click to expand...

Joey,

I think I know what your problem is because I just went through the same thing...and if I'm right - relax, because it isn't expensive.

First, a question - are you noticing your brakes a little spongy too? I had this happen to me, and it's the same problem causing both symptoms.

Lift the hood while the engine's running and see if you hear a hissing sound. That'll be the vacuum leak and it's probably coming from the brake valve right by the master cylinder. It plugs in toward the firewall, and it's a cheap plastic thing that's worn all the way around. Be careful taking it out becaue if it snaps off you'll have a beotch of a time getting the piece out of the receptacle.

Anyway, the part is in the motormite section of Autozone - $3.99. Takes all of 14 seconds to fix.
 
actually my brakes are acting alil spongy too. i just thought that i need to get new rotors. cause the last time i had the rotors cut, the mechanic said that they can no longer be cut. so i am actually upgrading the front brakes pretty soon. i will def check out what you suggest, i really appreciate it.
 
That little plastic thing is called a check valve. I would also recommend that you pull the brake booster vacuum line off, but wait until after you shut the engine off. This is to check and see if the booster is holding vacuum. If you don't here a nice whoosh after you pull the line off, you could have a bad check valve, or brake booster.
 
ill will keep you all updated. it has been waaaay too hot outside this week to do any troubleshooting. it feels like 120 degrees out!
 
I know what you mean. Pretty hot here too. Don't wait on that fix, though. I almost had 2 accidents b/c of my spongy brakes!
 
update: i replaced the TPS and while was in there, cleaned the throttle body as well. ( there was A LOT of carbon build-up in their ) after driving around, the issue still persists. it can not be a slip in the transmission, because when i gun it, i bust through the gears perfectly! only when im cruising and keeping at a constant speed, the RPMs just jumps. the only thing i can possibly think of is either a vacuum leak, or the PCM acting retarded? anyway, here are the things i replaced trying to resolve this.

new plugs and wires
stall converter
shift kit w/ a trans cooler
IAC valve
MLPS
TPS
had the transmission flushed couple times.
seafoam treatment
 
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