View Full Version : Very Rough Idle after 5AFE Swap - Please Help :(

01-01-2009, 11:08 PM

I just finished a 5AFE engine swap in my brothers 5th Gen Celica ST however it is running very rough at idle. Here are the things I know/tried.

1. I have a pretty large pre-o2 sensor crack in my exhaust manifold. Would a
large crack cause problems like this?
2. I have a disconnected ground wire that connects to drivers side fender
close to the charcoal canister. It's connected to the frame, but I don't
know what is was connected with to begin with.
3. The car does idle, but roughly. I can rev the engine very smoothly, but half
the time when I let off the gas the engine shuts off.
4. The car's timing was set to 10 degrees BTDC after it warmed up.
Unfortunately, it didn't help. That means the timing belt is ok right? The idle control seems to be working because part of the roughness is caused by the engine trying to speed up to keep itself alive. When I jumped TE1 and E1 to adjust the distributor the engine REALLY had a hard time running.
5. I have played around with the idle screw, but it doesn't seem to help.
6. My rough idle is around 800-900RPM

I am going to check for CELs then vacuum leaks. If anyone can think of anything else to try please let me know.


01-01-2009, 11:18 PM
When I short TE1 and E1 it sounds like a relay flips over by the P/S pump, then the check engine light starts flashing about 2 times a second which I understand to mean there are no stored CEL codes :(


Oh, when the key is still in the on position and I remove the TE1 and E1 jumper I hear a little pumping sound, again over around the p/s pump, which clicks for about 8 seconds then turns off. I have no idea what this could be either :(

01-02-2009, 01:39 AM
sounds like u dint hook up a vac line or a vsv

01-02-2009, 02:11 AM
Thanks for the help 85gtsblackman. I really appreciate it as this has got me scratching my head :(
I'll start double checking my VSV install again :P
I have been looking for a disconnected vac line for the past few hours but haven't been able to find one. I'm going to get a propane torch tomorrow to do a gas check... but I'm starting to suspect that my timing belt has skipped a tooth :(

Oh yeah, I forgot to mention that I replaced my timing belt, waterpump, and clutch during the swap. I've installed a 3SGTE timing belt before so the 5AFE timing belt was a piece of cake. The cam marks and teh crank's 0 TDC lined up perfectly after the tensioner was engaged and the crank was turned by hand a few times.

Can anyone confirm that a tooth skip is possible even when my timing gun is showing 10 degress BTDC on a warm engine?


01-02-2009, 02:37 AM
Whoah! i just noticed that the 5AFE came with green topped injectors whereas the 4AFE has grey/tan topped injectors. I used the 4AFE injectors with this install because of simplicity, but now I'm thinking it might be part of my problem. Anyone know if this would be a problem for sure?


01-02-2009, 03:07 AM
Scratch the injectors. I did swap over the green topped injectors that came with the 5AFE (they were higher flow anyway). However, it didn't fix my problem :(

Man... my timing is bouncing all over the place when I don't have E1 and TE1 jumped. I can time it to 10 degrees BTDC but when I take the jumper off it bounces between 0TDC to 15 TDC while idling around 950rpm :(

01-02-2009, 04:15 AM
is your water temp sensor working?

01-02-2009, 05:01 AM
andy10889: I suppose I could do an electrical check to find out :) I pulled the entire coolant neck off of the donor 4AGE which was working except for the spun bearing ;)
But that doesn't mean it wasn't in bad shape when I took it off. I'll take a look at it tomorrow.

Other suggestions for things to check on are appreciated :)


01-02-2009, 05:47 AM
The ground strap, I would bet, is supposed to tie to your transmission -- your poor idle might be a simple matter of insufficient grounding.

01-02-2009, 05:57 AM
Thanks for the suggestion Galcobar. I have got a very large ground strap going from the transmission housing to the negative side of the battery, so I'm pretty sure I've got the tranny covered, but it's possible the transmission was grounded twice. I know that's probably the starters return path so I made sure I kept track of it's primary ground strap :)

The mystery ground strap is only 2 feet long and has a pretty large ringlet on the end, so there are only a few places it could go. I'll keep looking around :P

Thanks again

01-02-2009, 06:14 PM
Alright, so the first thing I did today was check my timing belt install. Since I couldn't get a good angle of the cam gear alignment mark from the passenger side, I remove the valve cover and stuck a bobby pin through the cam gear and took a picture.


This is with the crank pulley at 0 degrees BTDC (or just a hair past it) (the real alignment mark is in the middle of that white glob)

It looks pretty dead on to me. Seems like it would be much farther out of alignment if I had skipped a tooth. Anyone want to give me a second opinion?

Exhaust crack picture to follow.


01-02-2009, 06:37 PM
Here are some pictures of the exhaust manifold crack. I don't think it's really important, but I just want to cover all my bases.


01-02-2009, 06:58 PM
I have a really simple question that I pretty much assumed when I bought the engine... I am trying to run the 5AFE engine with my 4AFE ECU because everything I read ahead of time says this engine is "plug and play" when you bolt all the 4AFE accessories to it. Did I misunderstand plug-and-play? Do I need a 5AFE ECU?

01-02-2009, 07:00 PM
u dont my 2nd engine in my stx was a 5afe, and i put it togather myself

01-02-2009, 07:04 PM
Thank you for the confirmation 85gtsblackman :)

01-02-2009, 11:22 PM
Is the crack bad enough that it is leaking?

01-03-2009, 12:30 AM
92-gt: Yes, It leaks. I'm looking at getting another one ASAP.

Well, as i=I expected, this problem ended with me finding something simple that I did wrong. Check this out


Pretty bad eh? It was installed on cylinder #4. It was a brand new plug, but I'm sure I didn't check it before installed it. After I installed a new new plug properly gapped the engine worked just fine. I normally double check my gaps when playing with my 3SGTE, but I got sloppy when dealing with my brothers car :)

Sorry to waste everyones time. I DO really appreciate everyone who tried to help me figure out my dumb mistake.


01-03-2009, 05:18 AM
i was gonna say check the plugs but i just got home from work, yeah it may have gotten dropped, my buddy did that when he was helping me work on my gts, dropped the plug and went to put plugs in 2 days later and forgot, i went though almost the same ordeal as you.

the crac wont really hurt anything, i had a stx that had a cracked manifold for 2 years before i replaced it. a header can be had almost for the same price as a manifold on ebay.

01-03-2009, 05:52 AM
Thanks for the tip. I'll be looking for a header soon :)

01-03-2009, 06:01 AM
Well as joe said, it wont hurt anything horribly, but it will decrease back pressure and could lose some power, ask ciento44 about that..

Glad you found the problem though!

01-03-2009, 06:09 AM
its a 5afe, if u fix the crack u may gain 1 hp