Limp Mode Issue — Any thoughts?

I am having limp mode issues with my B9 S4..

I have 9,000 miles on the car, did first oil change at 1500 miles & scheduled for 10k service this Friday. Roc-Euro intake installed at about 5,000 miles.

Past couple of weeks the car has displayed «drive system malfunction», rough idling and acceleration 3 times.. Each time the car is usually idling or parked. I shut the car off and turn it back on and it drives fine. I did have a CEL after though, but it went away after about +/- 60 miles. This issue happened again today, twice.. and now the car is driving normal with a CEL.

Is this the radiator fan issue? Could the Roc-Euro intake be causing a problem? I will be removing the intake and bringing the car to Audi on Friday regardless..

I am having limp mode issues with my B9 S4..

I have 9,000 miles on the car, did first oil change at 1500 miles & scheduled for 10k service this Friday. Roc-Euro intake installed at about 5,000 miles.

Past couple of weeks the car has displayed «drive system malfunction», rough idling and acceleration 3 times.. Each time the car is usually idling or parked. I shut the car off and turn it back on and it drives fine. I did have a CEL after though, but it went away after about +/- 60 miles. This issue happened again today, twice.. and now the car is driving normal with a CEL.

Is this the radiator fan issue? Could the Roc-Euro intake be causing a problem?

My opinion is that it is likely not the radiator fan. None of the users on this forum who have been affected by the radiator fan problem have reported either rough idling or a CEL absent a limp mode condition, at least that I have heard of.

The Roc-euro intake looks like it’s literally just a cheap $30 AEM universal round air filter bolted to a custom bracket somebody prefabbed and then marked the whole thing up to $200 on their generic Shopify site. It looks like almost zero engineering or R&D effort went into it at all (beyond making that bracket), so yes, in my opinion there is a good chance this could be causing issues.

Or it could be something else entirely. We’d need to know what codes you’re throwing to tell you more.

This is certainly one option. However, be advised that if the dealer see anomalous intake temps/O2 sensor readings/etc then it may either lead them on a wild goose chase of wanting to replace O2/temp sensors or other parts that are in actuality just fine, but that are throwing lights because a low-quality intake was causing sensor values outside what the computer expects. This may cause them to suspect modifications were done which could lead to a warranty denial scenario where you could at minimum be charged for the diagnostic visit. They may even suspect mods right up front when they pull codes and see that sensors showed X value for a several week period but then magically returned to Y value the day before you came to the dealer.

My advice would therefore be:

1. put your stock airbox on
2. pay an independent Audi mechanic to pull your codes (or pull them yourself if you have a scan tool), and clear them. You could post the codes here for some further thoughts if you like.
3-A. If the codes are indeed intake/temp sensor/o2 sensor related you can then drive on the stock airbox and see if the idling issue persists/CEL returns. If it doesn’t you’ll have solved your issue.
3-B. If the codes are fan related, then boom you have your answer on that.
3-C. If the codes suggest neither, you can at least make a more informed decision about going to the dealer and what you want to tell (or not tell) them. That said, your dealer is going to scan for codes at each visit whether you like it or not as part of their multi-point inspection.

TL;DR — I recommend that if one suspects their CELs may be due to mods, that one does not go to the dealer until they are sure they aren’t.

I am having limp mode issues with my B9 S4..

I have 9,000 miles on the car, did first oil change at 1500 miles & scheduled for 10k service this Friday. Roc-Euro intake installed at about 5,000 miles.

Past couple of weeks the car has displayed «drive system malfunction», rough idling and acceleration 3 times.. Each time the car is usually idling or parked. I shut the car off and turn it back on and it drives fine. I did have a CEL after though, but it went away after about +/- 60 miles. This issue happened again today, twice.. and now the car is driving normal with a CEL.

Is this the radiator fan issue? Could the Roc-Euro intake be causing a problem? I will be removing the intake and bringing the car to Audi on Friday regardless..

I had the RF issue — nothing like you’re describing happened at all.

I’ve asked this on several occasions since 2002: Please send me money, your money. Here’s why: MOST (over 51%) of the aftermarket «modifications» (technical term: CRAP) that we (and that includes me, in my younger years and for several of my 33 Audis) are tempted to buy usually have the unintended consequence (at least I sure hope it is unintended) of degrading the performance of your relatively big-buck car. Now, if it was actually someone’s intention to downgrade the performance, well, I take it back. Moreover, another dandy side effect of these aftermarket modifications is to dial back the «reliability» and therefore one would assume «durability» of these highly engineered machines. Again, if someone really intends to make their car less reliable and less durable, I take it back.

God, I hope it’s not too late for this next part.

Restore your vehicle 100% to its OEM build — nothing, not one thing should be out of place — do this BEFORE returning to the dealer. Make sure there are no decals, receipts, fingerprints, DNA for pity’s sake anywhere that a forensic team could use against you to deny this and ALL FUTURE warranty claims.

Say as little as possible, answer a question, if possible with «yes» «no» and «I don’t know.» Do not opine. Do not question.

The Roc-Euro intake is — from my highly opinionated perspective — the cause of your issues.

Read the following carefully: «Been there, done that.»

Only ONE time (OK, two) did ANY modification I ever made to my Audis pan out: I bought a new A8 in 1997 (waiting almost a year for it to come in — in Pearl White Metallic). I had read an article about a FACTORY sport suspension option that was offered (but not in the US). I ordered the parts and had them shipped from Germany (in the original Audi boxes) to the dealer. The dealer replaced the OEM (US) suspension with the German Audi A8 Sport-suspension. Had an all-wheel-alignment afterward and no issues. Likewise, I had a 2003 allroad and I ordered the OEM sport rear anti-swaybar. Had the dealer install that one too. Other than a slight buzzing when the air suspension adjusted itself since the sway-bar was slightly thicker and was up against the compressor for the air bladders, there were no issues with that one either.

Any time I made any attempt to do ANYTHING that would (presumably) improve HP or torque or both or anything relating to the motor or the electronics, bzzz! thanks for playing.

Please, send the money you would use on such modifications to me — I will write up something that sounds really really sexy for your Audi and send you «the part» in a box and advise you to put it in the trunk of your car, since it most likely will be a bluetooth device of dubious origin.

I’m outta my leage here — y’all have so much money you can, over and over and over again, buy a $60K car and before the fuzz is off the tires, you’re dumping money into «modding» the damn thing. Please dump the money into my account, for clearly you guys don’t need the money. But, I’m working on propping up my retirement income, and I would really appreciate your help.

Oh, almost forgot. If you make any change (well, almost) to your Audi and the dealer detects it — you can kiss your warranty bye-bye. I promise the thing I will send you will not void your warranty — bluetooth, remember.

OK, seriously — return the car to factory set up. See if that doesn’t help. If it does and «all’s well» move on. If it doesn’t, at least you can take it to the dealer and probably not be declared «dead to Audi.»

I remain: Often wrong, never uncertain and advise you to always wear your rubbers.

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