willisjefferyl

After a recent head gasket change I got the infamous honda surging idle with cel on. Before the head gasket change, this would sometimes happen at first start up on super cold mornings but no ce . The car does the exact same thing (idles up and down) with or without the MAP sensor plugged up. This is what led me to believe this is culprit. Just ran the codes and got three short cel blinks confirming the MAP sensor. Before I purchase a MAP sensor is there any other things that could throw this code without it actually being the sensor?

Thanks

goldsy

Make sure all the air is bled out of the cooling system after the HG change, give your FITV and IACV a good cleaning. Remove both and take some throttle body, brake cleaner or simple green and give them a good soaking and scrubbing.

94civic420

I just changed my head gasket on my 94 civic dx as well and now it seems louder , I did get my head resurfaced and a valve job and 3 new exhaust valves but could that have made my car a little louder ?

willisjefferyl

Im about 90% sure the cooling system is good but will prob drain and do it again. Im just running h2o anyhow since the weather is staying above freezing. No waste of coolant either. Anything specific to watch/look out for while cleaning the IACV and FITV? Any gaskets needing replaced?

willisjefferyl

Hey 94 420, did you have any surging idle problems before/after the head gasket change? I didnt notice any difference in amplitude but it mine sounds way smoother, restored the hp, and stopped that sound like an aluminum can rattling around in the block.

Former User

Get all the water out of your cooling system and fill with a name brand 50:50 coolant. Otherwise, your engine will be destroyed by corrosion.

And then bleed the cooling system as per the service manual instructions.

And follow all of goldsy's recommendations - he's giving good advice.

goldsy

Park the car uphill or out the front up on jack stands and remove the rad cap. Run it for an hour or until you see no more bubbles with the heat on full blast, that will ensure the system is free of air.

As Ron said, get that damn water out of there and replace with a 50/50 coolant mix or you'll be replacing a rad in no time. Water is fine if you're losing coolant and it's only going to be used as a temporary band aid. Coolant has anti-corrosion properties that water does not.

As far as the gaskets go. It's recommended that you replace them. I did not replace mine and have had no issues.

willisjefferyl

Thanks guys! Yeah I was planning on putting coolant back in it. Had a bad coolant leak just prior to the HG change (air pushing all the coolant into the overflow). Coolant was going everywhere and had lots of light overheating. Just changed out the head gasket and wanted to run water for the first week to make sure everything was running properly. So far so good, well except for the idle surge ( fluctuating about 500-700 rpms, up and down). Going to drain cooling and refill with coolant this weekend. I plan on cleaning the IACV as well as the FITV. When freeing the cooling sytem of air, should I ever use the bleeder valve at the head side of upper radiator hose?

94civic420

It's idles a little low and kinda jumps around like low idle then higher then low
No tack so can't tell the rpms

BrakeExpert

Oy. First off, the engine is aluminum, nothing will "corrode". Coolant drops the freezing point AND upps the boiling point. Pure water WILL boil out of the car, you'll have to refill it every five minutes, and the excess pressure of steam can blow your new head gasket, if it already hasnt.

Fill the car with 50/50 water/coolant. Turn the heater in the car to "hot", crank the engine with the radiator cap off. When the coolant level drops, add more. after about 5 minutes when it starts dropping, put the cap on. This isn't an Odyssey, you do not need to bleed it on a hill.

By the way, the amount of coolant will not affect your engine's idle speed unless theres a leak.

replacing a head gasket...don't cheap out on 7$ worth of coolant when the pure water is more likely to warm the damn cylinder head.

Former User

Sorry, but this^ is just plain wrong. Aluminum definitely does corrode. It forms aluminum oxides, a chemical process that is accelerated by metal ions present in tap water (galvanic corrosion) and by the high temperature of the engine.

Never put water in your cooling system. Use a 50:50 coolant premix that contains anti-corrosion additives.

willisjefferyl

I thoingGuys, no need to argue. Ive ran water (alone) in many cars, many times for short periods with no damage. I know what happens to aluminum and I know how the cooling system works. The thread is on a MAP sensor code being thrown at the ECU. This is leaving me with the CEL on and a surging idle problem bouncing from 700 rpms to about 1500rpms In all due respect for the great advice, the cooling had already been bled air free, no bubble in the radiator. This was a huge issue before the HG change so Im aware of this issue in Hondas. I think the issue is with the IACV or FITV or maybe the MAP sensor is bad. Its a Denso sensor, which are like $15 new on ebay so Im doubting this is the Honda OEM part. Figured these guys are just cheap made and prob doesnt last. Any thoughts on these sensors?

Former User

I see no compelling reason to think that the MAP sensor is the problem.

The way your first post is written, you unplugged the MAP sensor and then you found code 3 thrown. Unplugging the MAP sensor would throw code 3. If you reset the ECU and don't unplug the MAP sensor, is code 3 ever thrown again?

The problem sounds more like an intake air leak or IACV, FITV, TPS, or ECT problem. It could also be caused by air in the cooling system or a misadjusted idle.

willisjefferyl

I got the code before I tried runinng the car without the sensor plugged in. With it plugged in and without it plugged in, its simply running exactly the same. Its almost as if the sensor isnt doing anything at all. before I changed the hg, there was no surging idle and no cel on. Altho, the idle did surge randomly on super cold mornings but no cel. And thisnwent away as soon as thencar warmed up. Now it does it anytime the car is in neutral, park, and sometimes in gear but at a stop. There is also a slight decrease in acceleration right before it picks up speed. Once it gets going, it runs great. This doesnt seem to be affecting gas mileage either.

Former User

Reset the ECU to see whether code 3 returns.

willisjefferyl

So today I had some extra time to clean the iacv and fitv. Put them back on and changed out the water for some fresh 50/50 coolant mix. Started the car, the ide was smooth. I was fairly excited. Drove down the road and back only to find the idle jumping up and down again. Disappointing to say the least. Reset the ecu, started the car and the cel came right back on as soon as the idle surged. Any thoughts?

willisjefferyl

Just wanted to follow up on the surging idle problem I had that seemed like forever. After cleaning IATV, FITV, checking the ECT, TPS, and MAP sensor(the only thing I was getting a code for), switching out MAP sensors, trying to adjust throttle (nearly impossible when you cant idle), and getting a new O2 sensor (due to recent one being seized in old intake manifold), I decided to look into the wiring. After a long boring process of tracing wires from the sensor to the harness, I found the a break in wires to the MAP sensor. I kept tracing the wires and found another 3 breaks in the same wire. Looked like a previous mechanic ( a shi**y one at that) pieced this wire together with 3 different sections of wire. Needless to say they must have pulled apart, triggering the code on the ECU and causing the infamous surging idle. I replaceed all the sections with on section, hooked it back up, and voila! purrs like a kitten. Headache is now gone.